Water Quality in Lakes and Streams

Background: 

Barnum is unique from other Denver Lakes in that is the only significant sized pond that functions as an “on-line” reservoir. While only 4 surface acres in size, Barnum is on the receiving end of an 1100 acre residential/commercial use watershed. The through line for the watershed and pond is Weir Gulch, originating several miles upstream (west) in Lakewood. The lake serves as  a water quality mitigation facility for the Gulch which reaches the South Platte River a half mile downstream from Barnum Park. 

Quick Facts: 

• Location: 360 Hooker St
• Acres: 4
• Typical & Max Depths:  ~1.5 & 4 ft
• Inflow Subsidies: Weir Gulch & Storm runoff
• Primary Values:  Good wildlife habitat; bird watching opportunities; storm-water quality and flood mitigation
• Wildlife Habitat: Good
• Primary Functions: Storm water retention; natural area habitat; open space opportunities (wildlife viewing)
• Potential Regulatory Issues: Dissolved Oxygen

2025 Update

View the full report with figures and references here.(PDF, 562KB)

Barnum’s primary assets include wildlife habitat, urban storm-water quality mitigation, storm water quantity retention, and wildlife viewing. Additional runoff was routed to the lake from Federal Blvd to help improve the quality of water discharged to the South Platte River. This project also helps slow runoff to the river during large rain events. This is a hard working pond which reflects the history and resilience of the neighborhood.

The large storm-runoff-basin to pond (acreage) ratio results in a sediment load capable of converting Barnum from a pond with up to 4-foot depth, to more of a wetland with less than a foot depth in less than a decade. Erosion and sediment movement within the Weir Gulch channel is severe when this storm basin experiences an extreme rain event, as we had in 2013.The lake can be further challenged with drought conditions that leave it very shallow, allowing the rooted plants to proliferate, throughout the pond and the perimeter vegetation to encroach on the pond. All of this growth contributes to the organic load and sediment as it dies back in the fall and decomposes.

The most pressing challenge for Barnum Lake is sedimentation as discussed above. This results in quick filling of the ‘lake’ resulting in extremely shallow depthsto 2 feet) without a sediment removal project every 10 years. The high load of sediment and organic material reaching the lake via Weir Gulch includes material from residential yards, roadways, commercial, and industrial areas. However, a significant portion is coming from erosion of Gulch banks for several miles upstream of the pond Additionally, the high productivity within the lake (plants and algae) results in an annual deposit of organic material that dies and decays on the lake floor. All of this equates to thick, rich sediment which maintains shallow conditions and assures high nutrient loads to support summer plant and algae growth.

This combination of factors converts the ‘lake’ into more of a functioning wetland. The definition of a wetland according to our US Fish and Wildlife Service includes: surface acreage less than 20 acres, shallow depths (<8 feet); and dominated by rooted plants (i.e., >30% of pond-bottom with emergent vegetation – such as cattails and bulrush). Wetlands are also prone to occasionally draw down leaving sediment exposed on extremely dry years. Barnum does meet these criteria, making it arguably more accurate to refer to it as a wetland and not a lake or pond.    

Water Quality:  Regardless as to whether Barnum ‘Lake’ fits the definition of a wetland, for now, it is regulatorily considered a lake and is therefore held to water quality standards of other lakes within our region. Currently, Barnum is on the State’s list of exceedances for one issue - dissolved oxygen (must be >5mg/L). The past five years monitoring should justify removal of Barnum from this listing. There was concern that contributions from the 2011 Federal Blvd storm runoff capture and discharge (to Barnum) would result in deteriorating water quality within the lake.  Our data suggests that so far that has not been the case. The median value for E.coli decreased significantly from the ten years prior to the project compared with 12 years afterwards. Both nitrogen and phosphorus also decreased when comparing the decade before and then after the project. 

Ecology/Habitat:  Barnum is shallow, mostly less than two feet throughout the water body.  This results in rooted plants throughout much of the wetland, encompassed around the perimeter by a ring of emergent vegetation (mostly a mix of cattails and bulrush).  By mid-summer, the rooted plants (usually dominated by Potamogeton, or pondweed) are typically covered with a moderate to high amount of filamentous green algae.  While not toxic, some species can spread rapidly and become a nuisance for humans and wildlife.  Hydrodictyon (water net) is particularly disruptive and difficult to manage.  Barnum has experienced this sporadically over the past five years.  Duckweed is a small flowering plant that floats on the surface.  While commonly found on Barnum it does not blanket the lake (as it often can) due to competition for space and nutrients with the other algae and vegetation.

Wildlife:  Birds, primarily waterfowl and short- to long-legged wading birds are common wildlife found at Barnum. Avocets are generally rare around the City but can be very common at Barnum during mid-summer. These are elegant mid-length legged wading birds which specialize in feeding on aquatic-insects in shallow mud-flats. A wide variety of ducks and passerine birds are also routine residents and visitors at the lake. 

Recommendations

Short term:

• Annual community park and lake cleanup events sponsored by DPHE and/or DPR
• Track and use control measures on algae or plant growth considered destructive to aquatic and public health, such as Hydrodictyon and/or blue-green algae.

Long Term:

• Current DPR/DOTI planning efforts on Weir Gulch could help mitigate some of the sedimentation problems in Barnum. Capturing sediments where they begin will help decrease sediment loading and maintenance needs (frequency of sediment removal).  This will also help decrease nutrient and contaminant loading in the lake.  We strongly support efforts to stabilize the Weir Gulch channel through southwest Denver and upstream;
• As opportunities arise, conduct sediment removal from the main water body.  This could happen during drought years when water levels make the lake more amenable to manipulations necessary for sediment removal options (i.e., coffer dams and heavy equipment accessing the lake bottom);
• Re-establish a more functional sediment forebay on the south end of the ‘lake’, immediately downstream of the bridge; and
• Consider wetland expansion on the south end of the park to help capture some of the sediment and associated contaminants from the upper watershed via Weir Gulch.

Background: 

Duck Lake was created in the 1890’s along with the other City Park water bodies, Ferril Lake and the 17th AvePond. Duck is unique from the other lakes in that it borders the Zoo and is therefore perfectly situated to serve as a living exhibit in addition to the other more traditional lake roles.The City Park ponds and lakes were sustained with additional water from urban runoff and the South Platte River/Chatfield Reservoir via City Ditch until 2002 when it transitioned to primarily recycled water. That transition was completed in 2004 when Duck Lake became the terminal lake on the end of a chain of Denver water bodies fed by the historic City Ditch, which conducts de-chlorinated recycled water from south of Washington Park on its journey to both Washington and CityParks. Within City Park, water flows into Ferril via the 17th AvePond, and then from Ferril into Duck Lake.

While the primary water source maintaining the lake is recycled, this subsidy water to Duck Lake is conditioned by its residence time in Ferril and other water bodies up-ditch. Duck Lake also receives storm runoff from the Zoo in addition to a significant amount of storm runoff reaching Ferril. Storm runoff from the Zoo is mitigated by a sand filtration set-up prior to reaching Duck Lake. If necessary, discharge from Ferril can be diverted around Duck Lake. Ultimately, discharge from Ferril and Duck Lakes reaches the South Platte River downstream of 38^th Avenue.

Quick Facts: 

• Location: 2100 Steele St.
• Acres: 5
• Typical & Max Depths:  ~7 & 10 ft
• Inflow Subsidies: City Ditch & Storm runoff (via Ferril Lake), Zoo
• Primary Values:  Good wildlife habitat; bird watching opportunities
• Wildlife Habitat: Moderate to Good
• Primary Functions: Significant nesting habitat for cormorants, feeding, loafing, nesting for other waterfowl; wildlife viewing for park and zoo visitors

2025 Update

View the full report with figures and references here.(PDF, 831KB)

The Duck Lake island is home to the 4th largest double breasted cormorant rookery in Colorado. The islands’ vegetation and shoreline were in need of attention due to prominence of weedy and invasive species. Denver Parks and Recreation (DPR) under-took a restoration project in 2023/24 to improve and create a more sustainable habitat, something that could better support the avian community that rely on the lake and island. The landscape was cleaned up, invasive un-wanted vegetation removed, and two artificial roost/nest poles installed. It is hoped that this will help provide quality nesting and loafing habitat for years to come.

Other developments over the past two years include an up-graded aeration system (2023) and addition of a set of five small floating wetlands (2024 - Fig 2). The aeration system appears to be functioning well.  The wetlands have over-wintered and as of this report, it’s not clear whether the plants will come back on their own or if a more active spring cleanup and re-planting effort and re-planting effort is needed. At a minimum, they will make nice habitats for waterfowl and turtles to utilize. This in turn provides wildlife viewing opportunities for park and zoo visitors. 

Water Quality:  

Water quality in Duck Lake is influenced by several factors, most notably high nutrient inputs driven by intensive waterfowl activity. Additional nutrients and organic matter enter the lake through stormwater runoff from the Zoo, surrounding park roadways, and inflow from Ferril Lake. These inputs fuel high algae and plant productivity, including filamentous algae, phytoplankton, and occasionally dense duckweed mats that can blanket the surface and limit light penetration.

Historically, those productivity swings contributed to low dissolved oxygen conditions—particularly in 2018–2020—when rooted plants, filamentous algae, and duckweed reduced light and increased oxygen demand in the sediments. Dissolved oxygen levels have improved since aeration upgrades in 2021 and 2023, with mid-summer measurements meeting state standards for the past five years. Ammonia levels have also improved over the last six years and are no longer classified as a regulatory exceedance, partly due to shifts in nitrogen chemistry driven by higher oxygen and pH conditions.

Copper levels remain a management concern. Copper-based algicides have been used for many years to control algae, resulting in periodic exceedances of state copper standards across several sampling years. However, the City is actively testing alternative strategies—such as biochar, floating wetlands, dye treatments, and phosphorus inactivation—to reduce reliance on copper. Taken together, these actions indicate an improving water quality trajectory, with further gains expected as alternative management tools mature. 

Recommendations

Short term:

• Continue with algal screening and whatever short-term actions are needed regarding algal community status. This could include cyanotoxin testing and advisory posting if necessary, algicide applications, or other options;
• Assess effectiveness of floating islands and whether they provide a habitat function worthy of maintenance needs to sustain them.

Long Term:

• Duck Lake has been a great testing ground for management alternatives (i.e., biochar, dye, floating islands); track effectiveness of these strategies and consider new options.  Barley straw would be an interesting option combined with the upgraded aeration system and chronic blue green algae presence;
• Track biological and physical indicators of the island pertaining to the newly installed artificial nesting structures, landscape improvements (desirable species versus less desirable), and any other factors considered critical to long term sustainability (i.e., erosion along the island shoreline).

Background: 

City Park in central/northeast Denver offers many amenities: the Denver Zoo, a regional park with expansive amounts of turf fields, tennis, hand ball, horseshoes, walking and biking lanes, and three ponds ranging from 0.5 to 24 acres. The ponds were constructed and filled in the 1890’s. The largest of the three, Ferril, is sustained with recycled water via the 17^th Avenue sediment pond. The lake also receives a significant amount of storm runoff from the largest storm-water basin in the City (Montclair Basin – 3700+ acres) which originates in southeast Denver. Ferril Lake in turn overflows into Duck Lake to the northwest. If necessary, this water can be diverted around Duck Lake. Ultimately, discharge from Ferril and Duck Lakes reaches the South Platte River downstream of 38^th Avenue. 

Quick Facts: 

• Location: 2100 Steele St.
• Acres: 24
• Typical & Max Depths:  ~5 & 8 ft
• Inflow Subsidies: City Ditch & Storm runoff
• Primary Values: Open space and bird watching opportunities; storm-water quality and flood mitigation; recreation (fishing, pedal & paddle water-craft); park irrigation.
• Wildlife Habitat: Moderate
• Primary Functions: Park irrigation, regional recreational amenity (fishing, relaxing, open space), flood mitigation

2025 Update

View the full report with figures and references here.(PDF, 749KB)

Ferril Lake functions as a major recreational and visual amenity in City Park, offering opportunities for fishing, paddle and pedal boating, wildlife viewing, and open space enjoyment. Its restored historic lighted fountain, originally built in 1908, creates summer evening light-and-water shows that are unique within the region and enhance the park’s seasonal cultural programming. Habitat considerations include shoreline erosion along unarmored segments of the east and north perimeter, which is driven by wave action and heavy use, as well as the need for periodic island maintenance to sustain vegetation and support loafing and nesting birds.

Water Quality:  

Ferril Lake receives recycled water via City Ditch and a substantial volume of storm runoff from the Montclair Basin, which drains more than 3,700 acres of southeast Denver. While this water source carries higher salt content than other ditch systems, monitoring shows chloride concentrations remain far below levels that would affect sensitive aquatic species or park landscapes irrigated with lake water.

Over roughly the past decade, Ferril has shown notable gains in meeting state water quality standards. Dissolved oxygen and pH—previously areas of concern—have been within regulatory thresholds for the past six and seven mid-summer monitoring seasons, respectively. Declines in chlorophyll-a since 2018 suggest lower algal productivity, contributing to reduced pH variability and improved aquatic conditions overall.

Ferril also exhibits a distinctive water chemistry profile characterized by a relatively high nitrogen-to-phosphorus ratio. This suppresses competitive advantages normally held by blue-green algae under nitrogen-limited conditions and favors green algal species, which tend to be more ecologically desirable in urban lakes. As a result, Ferril’s phytoplankton community is generally dominated by green algal taxa rather than nuisance blue-greens, further supporting clearer water and healthier dissolved oxygen dynamics.

Recommendations

Short term:

• Continue routine observations to assess functional status of aeration and mixing units as well as algal productivity (DPR and DPHE);
• Assess island landscape and shoreline integrity;
• DPR should continue their current efforts from the past few years. Ferril is doing well.

Long Term:

• Assess shoreline around the lake perimeter and the island, consider options to stabilize it.  This could provide many benefits, some of which include: enhanced aquatic and terrestrial wildlife habitat; decrease negative impacts from bank erosion on water quality (additional nutrients, decreased water clarity) and subsequent algal growth; improved recreational experience – stable banks; and sustainable landscape approaches.
• Consider a variety of bank stabilization approaches with priority to interactive ‘organic’ approaches where possible (i.e., vegetation – both aquatic and upland such as bulrush and willows respectively).  Some boardwalk options could also diversify recreational options to lake visitors.

Background: 

Green Valley Ranch (GVR) was transformed from a working ranch northeast of Denver into a vibrant Denver neighborhood with over 40,000 residents at this time.TheGVR Pond is in north GVR within the Town Center Metropolitan District, adjacent to the GVR Recreation Center. The pond is a shallow 5-acre urban pond with minimal storm water inputs from the immediate park surroundings, a 40-acre residential storm water basin, and possibly a small portion of runoff collected from Argonne Way. 

Some lake management tasks for the pond were taken on by Denver’s Department of Parks and Recreation (DPR) in 2023. To support DRP’s efforts, this was the first year that The Denver Department of Public Health and Environment (DDPHE) conducted a formal lake monitoring visit during DDPHE’s annual mid-summer (July-August) trend monitoring efforts. 

Quick Facts: 

• Location: Argonne Way at 50th Ave
• Acres: 5
• Typical & Max Depths:  4.5 ft, 5 ft
• Inflow Subsidies: Limited road and residential storm runoff
• In-lake Issues: Elevated nutrients, blue-green algae blooms, limited habitat
• Wildlife Habitat: Limited
• Primary Functions: Community center, natural space

2025 Update

View the full report with figures and references here.(PDF, 604KB)

Although there was an aeration system installed in the pond to combat algae, the shallow depths and minimal sized installation render it of limited value as reflected by intense annual blue-green algae blooms in 2022 and 2023 (Fig 3). Several blue-green algae taxa were identified from DPHE’s algae surveys conducted in 2022 and 2023 (Fig 4). 

Algae blooms were also the primary contributor to cloudy water (Fig 5) as exhibited by shallow secchi depths, elevated chlorophyll-a levels, and high pH (Fig 6). These factors are symptoms of excessive algae growth. One other monitored pond, AquaGolf, had similar characteristics. AquaGolf is a perennially challenged water body with limited inflow to turn over water, shallow depths, and plenty of nutrients. 

Water Quality:  

The GVR Pond scores poorly relative to other Denver lakes and ponds included in our long term analyses. This is based on a Eutrophic Index (Carlson 1980), nutrient levels, and frequency of blue-green algae blooms. The Carlson Eutrophic index is driven by phosphorus concentrations, water clarity (secchi depth), and phytoplankton activity (chlorophyll-a). Among all monitored Denver Lakes, GVR Pond was ranked alongside two additional lakes with the highest eutrophication values (Fig 7). This is due to the very high phosphorus concentrations along with low water clarity. Eutrophic to hypertrophic classifications are expected in shallow urban ponds in the Denver region.

Habitat and Wildlife: The habitat from upland to in-lake is limited. Starting upland, the perimeter is dominated by high maintenance turf grass with a scattered fringe of weeds, shrubs, and trees (Fig 7). Most of the perimeter shoreline consists of large boulders which provide some bank protection and may provide fish cover and feeding opportunities. In-lake there is limited habitat short of objects that have been thrown into the pond over consecutive years, and the aeration system. The latter may provide some sustenance (near the bottom aerator heads) to aquatic life when dissolved oxygen is low or during blue-green algae blooms. Wildlife habitat supports the minimal species of urban terrestrial animals, such as rabbits, small rodents, and passerine birds. Waterfowl and large wading birds (such as herons) may be attracted to the lake, but the poor water quality coupled with annual blue-green algae blooms make it less preferrable. These factors don’t promote adequate food sources or nesting opportunities .

Recommendations

Short term:

• Phosphorus mitigation (clay, char, phosphorus binding algicide), algicides as needed, barley straw, ultrasonic, and dye treatments are some suggested approaches that should be considered or continued (phosphorus binding algicide has already been utilized by DPR) to help maintain good conditions for aquatic and other wildlife along with residents and others that visit the park. These are all relatively short-term approaches that do not require a high amount of planning and coordination.

Long Term:

• Some relatively long-term approaches that could be implemented within the pond and the stormwater basin include: sediment removal; establish wetlands / forebays at outfalls to mitigate incoming storm runoff; watershed stormwater improvements; and outreach and education (parks and public-residential area).

Background: 

Overland Pond is the western portion of what was once the combined AquaGolf–Overland Pond lake, a single water body that was separated by a berm sometime between the 1940s and 1960s. Today, Overland Pond is a central feature of the Overland Pond Open Space, a natural area and park focused on native vegetation and wildlife habitat, with amenities around the pond that support fishing, scenic enjoyment, and bird and wildlife viewing. The pond is unique among Denver’s lakes and ponds because it is primarily supplied by a direct diversion from the South Platte River. This dependable water source supports a relatively robust wildlife presence, but it also introduces higher nutrient levels, particularly nitrogen and phosphorus, due in part to the diversion intake being located downstream of a wastewater treatment plant. Combined with the high rate of water turnover, these conditions strongly influence the pond’s water chemistry and biological communities.

Overland Pond has benefited from strong community and organizational partnerships focused on habitat improvement and water quality. Local neighbors and the Trout Unlimited chapter have contributed to habitat management and monitoring, including innovative pilot testing of genetic assays to better understand the pond’s fish community, expanding tools for assessing aquatic ecosystems. Additional enhancements were led by the Greenway Foundation and neighborhood groups, who helped establish native vegetation and supported a major pond restoration effort in the mid-2010s. This work included sediment removal, shoreline redesign, and construction of a pier, overlook, and improved shoreline access along the south side of the pond. Much of the natural area establishment was coordinated and carried out by the Denver Department of Parks and Recreation Natural Areas Program, with support from these partner organizations.

Quick Facts: 

• Location: 955 W. Florida Ave
• Acres: 1.7
• Typical & Max Depths:  ~5 ft, 7 ft
• Inflow Subsidies: South Platte River
• Primary Values: Irrigation supply (indirectly), wildlife habitat & viewing, and fishing.
• Wildlife Habitat: Good upland and aquatic
• Primary Functions: Good riparian tree canopy for a variety of birds and possibly other wildlife.

2025 Update

View the full report with figures and references here.(PDF, 651KB)

 Overland Pond has not experienced significant management actions over the past ten years. Sediment removal and replacement of the outlet structure (2014/15) were the last major management inputs into the pond. The surrounding park maintenance, stream renovations (South Platte River-2018/19), and diversion structure replacement have improved overall regional habitat both instream and along the riparian area. This also assured adequate water supply to the pond. These latter actions did not have direct impacts within the pond and its’ immediate perimeter. The sediment removal provided temporary improvements. However, the pond bottom sediment re-settled over the year or two following its’ removal and included sediment contributions from the inflows, possibly during a significant storm event in 2013. 

Water Quality:  

Water quality in Overland Pond is largely influenced by diversions from the South Platte River and upstream discharges from the South Platte River Renewal Plant, located about 1.5 miles above the pond’s intake. Improved nitrogen and phosphorus controls at the plant over the past 20 years have reduced nutrient inputs to the river and the pond, though nutrient levels and dissolved oxygen in Overland Pond are still strongly affected by inflowing river water and the pond’s high water turnover. This turnover makes it difficult to maintain balanced algae communities and healthy dissolved oxygen levels, which were below preferred levels from 2022 to 2024 but improved in 2025. Copper levels have occasionally increased following algae control treatments, but recent management practices have kept concentrations low.

Habitat and Wildlife:

Acre for acre, Overland Pond provides a significant amount of valuable habitat, supporting wildlife such as turtles, cormorants, kingfishers, and a variety of duck species, with water temperatures and dissolved oxygen often sufficient to support trout due to cooling from South Platte River diversions during the hottest months. The regular presence of kingfishers reflects the pond’s proximity to the South Platte River, where they are more common but will also forage in nearby ponds. Overland Pond’s algae and plant community is relatively subdued compared to other Denver lakes because steady river diversions create high water turnover, keeping plankton productivity low to moderate. This limits harmful blue-green algae blooms but also constrains beneficial algae, and adding in-pond fish structures could further enhance the pond’s fish habitat.

Recommendations:

• Moderate summer inflows if possible to allow a slower water exchange and subsequently higher algal productivity. This could enhance the beneficial algae species (i.e., chlorophytes such as Pediastrum spp., Coelastrum spp.). Subsequent impacts would be increased oxygen and food for other aquatic species.
• Consider aeration to provide assurance that aquatic life has adequate oxygen during periods of otherwise low oxygen occurrence.
• When necessary, assure there is an adequate habitat connection between the South Platte River and the pond. Enhance this connection however possible. Also consider how a habitat link can be enhanced with AquaGolf to the east of Overland. An example could be allowing for bypass under the fencing to allow reptiles, amphibians, and smaller mammals to cross the fence barrier.
• If not already present, add fish habitat structures to the pond to provide some cover, shade, and prey species (for fish) habitat.

Background: 

 Parkfield is a designed regional storm detention facility within a natural area in northeast Denver. Developed in 2003, this shallow prairie wetland serves as detention for a 2,660- acre storm-basin (Fig 1). This is one of the primary functions behind the design of the pond for which the only water subsidy provided to the wetland is stormwater inputs.The wetland is mostly less than three feet deep throughout with rooted vegetation covering 50% to 75% of the pond in mid-summer. Much of the vegetation serves as a base supporting excessive growth of attached filamentous algae. The floating plants duckweed and watermeal are also prevalent throughout the wetland covering much of the surface where filamentous algae is not present (Fig 2).While in some situations the excessive plants and algae growth would not support uses such as fishing, it is ideal for other functions. The high plant density helps to settle storm water inflows and improves the wetlands’ ability to mitigate suspended solids and contaminants. The high plant growth also provides great habitat for aquatic life; a bonus towards the natural area role of the wetland.

Quick Facts: 

• Location: Parkfield Natural Area at 1555 E 53rd Ave.
• Acres: 10
• Typical & Max Depths:  ~2.5 ft, 3.5 ft
• Inflow Subsidies: Storm runoff
• Wildlife Habitat:Very good
• Primary Functions: Storm water retention; natural area habitat; open space opportunities (wildlife viewing)

2025 Update

View the full report with figures and references here.(PDF, 525KB)

When viewed as a lake, the assessed water quality parameters that could be considered marginal for Parkfield are dissolved oxygen (occasionally low) and pH (sometimes high). The pH levels exceeded water quality standards on two of the past five mid-summer visits, while dissolved oxygen also exceeded it on one occasion (Fig 3). These two factors naturally fluctuate in wetland habitats due in part to the impact of excessive plant and algae growth, shallow depths, and rich organic sediments.More specifically, as plants and algae photosynthesize, pH in the water column is driven up (more basic). When pH exceeds 9.0 it can become stressful to fish and other aquatic life. Dissolved oxygen fluctuates daily and is impacted by multiplethings – including light penetration (blocked by surface plants such as duckweed), temperature, and oxygen demand (by decomposing processes and organisms such as bacteria) at the sediment water interface. These are all natural occurrences in a freshwater wetland.

Habitat and Wildlife:

Wetlands are highly valuable ecological habitats in the grand scheme of natural systems in our region. They offer quality shelter, feeding, and breeding locations for both aquatic and terrestrial wildlife. Frogs, salamanders, and aquatic insects all have great opportunities at Parkfield. Rare insects have been noted at Parkfield by both professional taxonomist and City biologists. Amphibians rely on wetlands to provide all the necessary components for sustenance. This in turn supports waterfowl, wading birds, and other wildlife. Emergent vegetation (cattails and bulrush) around the perimeter provides great cover for waterfowl such as ducks, grebes, and coots (Fig 4).

A disadvantage of the excessive plant and algae growth is that it does not support user-friendly fishing opportunities. That, coupled with the variable water chemistry of wetlands, make them less than ideal for maintaining a top recreational fishing resource. This is not a function to be expected from Parkfield. However, the wetland does support small warmwater species, likely fathead minnows (Fig 5). These fish along with amphibians and crayfish provide an attractive food source for larger animals such as Great Blue Herons and other long-legged wading birds. Trout and large warmwater species such as bass should not be stocked in Parkfield, or in any of Denver’s wetland habitats. 

Recommendations:

• Expectations of Parkfield should be consistent with its intended design, which was to providestormwater detention and wetland functions within the natural area;
• Denver has few natural areas anchored by a wetland with this capacity to provide wildlife habitat,connection to nature, and storm water mitigation. This should be valued and sustained for the uniquefunctions provided by a wetland of this size;
• Assure sustained low maintenance landscaping in the vicinity of the wetland to minimize nutrientinputs and encroachment on the wetland and its perimeter plant community; and
• Take advantage of this resource and utilize for education and volunteer opportunities within the localcommunity.

Background: 

Sloan’s Lake Park is one of Denver’s most visited parks and open spaces thanks in part to the opportunities it provides for metro-area residents and visitors. Because of its unique and elevated role, Sloans Lake has been a primary focus for the city’s Lake Management Team for many years. The large surface area, shallow depth, nutrient-rich sediments, and marginal quality urban runoff make Sloans highly productive and prone to summer blue-green algae blooms.

2022 Update

View the full report with figures and references here.(PDF, 811KB)

Over the past decade, blue-green algae toxin advisories have been a regular occurrence from late June through September. In response, Denver Parks and Recreation expanded its lake management strategies in 2022, most notably by using phosphorus sequestration with Phoslock, a clay-based product that removes phosphorus from the water and binds it in lake sediments. Along with other management actions, this approach contributed to improved water quality and resulted in the first summer in many years without a significant blue-green algae bloom.

Water quality trends had already been improving prior to 2022, despite ongoing algae issues through 2021. Increased water clarity has been observed in recent years, reflecting reduced algae activity and lower suspended sediment levels. In 2022, mid-summer water clarity reached its highest levels in the past 20 years. Factors contributing to these improvements likely include more effective algae control, the end of motorized boat use in the lake in 2020, the Phoslock treatment, and broader citywide investments in stormwater controls within the watershed.

New efforts in 2022 also included a full season of monitoring with two remote sensor units placed in different areas of the lake to provide real-time data on lake conditions and seasonal changes. Monitoring results showed clear benefits from phosphorus sequestration: no cyanotoxin advisories were needed during peak summer months for the first time in 11 years of monitoring, the phytoplankton community was more diverse and balanced, and phosphorus levels were among the lowest recorded in the past decade. Declines in both nitrogen and phosphorus following treatment suggest that Phoslock played a significant role, alongside natural seasonal patterns. 

Recommendations 
These recommendations will reflect some of the actions already being considered by the DPR and their multi-agency work group which is currently developing plans to maintain and improve Sloans in 2023 and beyond.

Short Term:

• Phoslock and Algae Control Applications: DPR plans to repeat Phoslock treatments in 2023 to further sequester phosphorus in lake sediments, with occasional granular or liquid algae control products applied as needed.

• Monitoring and Assessment: DPHE will support DPR with mid-summer monitoring, sediment analyses before Phoslock applications, and ongoing evaluation of treatment impacts in collaboration with DPR and contractors.

•  Data Collection Enhancements: In addition to qualitative plankton screening, DPHE will perform quantitative assessments, track nutrients, metals, and water chemistry, and take chlorophyll-a measurements to calibrate remote sensor data for improved lake management decisions.

Long Term:

• Sediment Removal/Dredging: DPR’s long-term plan includes removing or dredging lake sediment to deepen Sloans Lake, cool water temperatures, reduce nutrients, and limit conditions favorable to blue-green algae blooms.

• Benefits for Ecology and Recreation: Sediment removal is expected to enhance aquatic life, support fish populations, and improve recreational opportunities such as boating, fishing, and wildlife viewing.

•  Watershed Stormwater Management: Continued development of upstream stormwater facilities in Denver and surrounding jurisdictions will help improve inflow water quality by settling sediments and contaminants, particularly during flood events.

Background: 

 The Vanderbilt Pond was established after the 1930’s, likely related to building of major roadways in the area, such as Santa Fe Boulevard and Interstate 25. It was utilized as an industrial waste pond by Gates Rubber Company for decades until the early 1990’s. Mixed use in the area includes a park, commercial, residential, and transportation roles (Fig 1).

 The remnants of its industrial waste period have been naturally attenuating over the past 30 years. While it’s a slow process, conditions do seem to be improving ever so slightly by some measures. The typical urban impacts most Denver lakes receive influence this process. Illicit dumping and urban storm runoff contribute nutrients and contaminants that provide additional quality challenges toward management of the lake. Regardless, there is great potential for Vanderbilt Lake. 

Quick Facts: 

• Location: 855 S. Platte River Dr.
• Acres: 4.3
• Typical & Max Depths:  ~7 ft, 10 ft
• Inflow Subsidies: Storm runoff
• Wildlife Habitat: Poor to good
• Primary Functions: Good riparian tree canopy for a variety of birds and possibly other wildlife

2025 Update

View the full report with figures and references here.(PDF, 718KB)

 Noteworthy occurrences have included potential waste dumping of portable toilets since 2023/24 and a duckweed bloom in the summer of 2024 (Fig 2). The bloom was likely related to the waste dumping.  Development of the property east of the lake and on the east side of the South Platte River will impact use of the park. Residential and commercial development will bring many more people to the park. A bridge has already been built which will connect the park to the east side development. A women’s soccer team stadium has also been proposed for the space east of the river. All of this will increase park and lake visitors.

Water Quality:

Over the past 25 years, there have been noticeable improvements in dissolved oxygen levels in the lake. Between 2019 and 2023, four of five years showed higher oxygen concentrations in the upper half of the water column (~4 feet) and/or a reduction in the anoxic layer near the bottom sediments. While 2 mg/L is not ideal, it can sustain aquatic life, especially when oxygen levels are higher in the upper water column. Improved oxygen in deeper layers also helps accelerate the breakdown of contaminants in the sediment, supporting overall lake health.

However, the past few years have seen setbacks due to ecological events, particularly duckweed blooms in 2024 and 2025. Dense duckweed coverage reduced light penetration, lowering plant and algal productivity and leading to decreased oxygen levels, which culminated in a significant fish kill in 2024. The subsequent decomposition of duckweed and fish contributed to poor oxygen conditions in 2025. Low oxygen near the lake bottom also triggered the release of nutrients and metals, including ammonia, phosphorus, and manganese, which were elevated in 2025. These changes highlight how oxygen fluctuations influence nutrient cycling, metal concentrations, and overall water quality, with duckweed playing a key role in temporary uptake of some constituents.

Habitat and Wildlife:

The use of Vanderbilt as an industrial waste pond has its obvious drawbacks, but it can be argued that it had a silver lining of sorts. Vanderbilt is unique from all other lakes and ponds in Denver regarding its robust ring of riparian habitat rich in tree cover. This provides significant habitat potential for birds and wildlife that benefit from the overstory combined with the lake. The negative impacts are primarily a result of the accumulation of industrial organics within the sediment. As microbes feed on and breakdown these contaminants they utilize what little oxygen is available within the water column at the sediment-water interface. This results in an oxygen deficit, more intense anoxia (lacking dissolved oxygen) throughout the bottom half of the water column. These conditions are not supportive of a healthy aquatic ecosystem. Think fish, aquatic insects, and zooplankton, as well as the phytoplankton and algae that would support them.Over the past decade, plans were made to mitigate these accumulated sediment contaminants. Due to the multiple jurisdictions involved coupled with unknown development plans for the area, there has been no active management steps taken. In the meantime, the lake has been dealing with the contaminants on its own time through natural attenuation2. The microbes continue to convert contaminants to energy. While creating poor conditions in the bottom half of the lake, long term monitoring suggests there are improvements. The trend of anoxic conditions (D.O. <2mg/L) starting at four to five feet below the surface began to migrate and drop lower in 2019. Although it was extremely poor in 2024 and 2025, this was due to ecological processes beyond the sediment contaminants (duckweed blanket, see p1 and 2, Fig 3). In the long term, this perturbation may help with natural attenuation.

Recommendations:

• Most of the issues with Vanderbilt start with lack of dissolved oxygen throughout much of the water column. Effective aeration could drive the release of unwanted constituents from the sediment (nutrients and metals). This will require an aeration system effective at both (1) providing oxygen in the lower depths; and (2) mixing the entire water column. Another benefit of aeration would include water movement. This will make conditions less hospitable to blue-green algae and increase the chance of promoting beneficial phytoplankton. This in turn could support other ecosystem levels such as fish and zooplankton through provision of food and oxygen;
• Consider innovative alternatives that could achieve similar impacts as aeration;
• If another duckweed bloom blankets the surface, use it as a bio-remediation tool by letting it stand for two to three weeks, then harvest it to remove metals and nutrients accumulated within the plants (Zhou et al. 2023);
• Maintain a healthy, diverse riparian stand inclusive of trees: It is natural for a jurisdiction to seek significant improvements in locations such as Vanderbilt Park and Lake. Current development will include connection of newly built residential neighborhoods to the park. The increase in park and lake visitation will likely spur more immediate lake and park ”improvements”. While this could benefit the wildlife and local residents, doing so without removing existing habitat strengths is encouraged.
• There is a significant presence of invasive plants and trees making up the thick growth around the lake. Replacing these incrementally with native plants would help maintain the function of the existing vegetation while working towards a more preferred habitat long term. It is encouraged that this process be conducted in stages rather than a complete removal. This would help support what wildlife already utilizes the area but while working towards the goal of a healthy native riparian community.