Water Quality

Sloan's Lake Denver

Denver Department of Public Health & Environment has been monitoring the quality of water in Denver’s lakes and streams for more than 45 years. Over that time, the program has grown to include many other important aspects of water quality. You can learn more about what we do by exploring the topics below.

How You Can Help Keep Denver's Water's Clean(PDF, 609KB) 

Water Quality in Lakes and Streams

What is Denver Doing to Protect Water Quality

Denver’s goal is to have fishable and swimmable waters in all our lakes and streams. Denver’s Departments of Public Health and Environment (DPHE), Transportation and Infrastructure (DOTI), and Parks and Recreation are all working hard to ensure the City meets that goal. Here are a few things the City is doing to improve water quality in its streams and lakes:

  • DOTI performs routine maintenance on storm and sanitary sewers to eliminate cross connections and remove blockages. To date, the program has successfully reduced the amount of bacteria entering the South Platte River from the City’s storm sewers. It is still too soon to tell how those reductions have affected water quality in the South Platte River.
  • DOTI has identified areas where more facilities are needed to ensure storm water runoff is adequately treated to remove sediment, trash, and other pollutants. That information has been used to develop an implementation plan which describes and prioritizes opportunities for installation of water quality treatment facilities. For information on planned projects visit the Denver Public Works Green Infrastructure webpage. Information about facilities which have already been installed can be on the Green Infrastructure Story Map
  • DPHE samples the South Platte River and its tributaries to determine the impact of urbanization on water quality.  Monitoring is also conducted to determine if there are any public health risks associated with recreating in streams and lakes in Denver. Additional sampling of Denver’s lakes informs maintenance and management decisions. 
  • DPHE assess the effectiveness of actions taken by other City agencies to improve water quality.  Information from those assessments ensures that actions are effective, helps improve the design of future water quality interventions, and provides a better understanding maintenance requirements.
  • Parks and Recreation manages most of the City's lakes.
    Detention pond at the Joe Shoemaker School at Cherry Creek and Havana provides treatment for water quality prior to discharging to Cherry Creek

During storm events, the new detention pond at the Joe Shoemaker School at Cherry Creek
and Havana provides treatment for water quality prior to discharging to Cherry Creek.

Recreating in Lakes and Streams

Denver’s lakes and streams receive runoff from City streets, yards, parks, and discharges from industry and wastewater treatment plants. Sometimes pollution in the runoff and discharges, which includes bacteria such as E. coli, can make residents sick.

DDPHE does not recommend swimming, wading, or playing in City streams or lakes. Swimmers are encouraged to use the Denver Parks and Recreation swimming facilities throughout the city. Kayakers may also become ill from ingesting surface water. If you choose to enter one of the City’s streams of lakes, here are some safety tips: 

  • Wait 72 hours after a storm
    • Runoff from City streets is one of the largest sources of pollution in Denver’s lakes and streams. Waiting at least 72 hours (3 days) after it has stopped raining provides time for bacteria levels to return to safe levels.
  • Try not to swallow the water, and if you’ve been in the water ALWAYS wash your hands before eating.

Things to Avoid:

  • Waters near flowing storm drains - This water may contain bacteria or other pollutants that can make you sick.
  • Areas where the water is not flowing - The lack of flow allows bacteria to accumulate to levels that can make you sick.
  • Areas with trash and other signs of pollution such as oil slicks or scum - These signs may indicate the presence of disease causing microorganisms.
  • Significant algae blooms that resemble green paint - These areas may have toxin levels that can cause skin irritation or physical problems for both humans and pets. 

Check out these infographics on how you and your dog can stay safe when recreating in Denver's streams and lakes. 

Although fishing is allowed in Denver's streams and lakes, we recommend catch and release fishing only.

Latest Water Quality Results (May-Oct)

Person sampling water quality  

DDPHE samples streams and most lakes in Denver at least once a year. Results from samples collected at the following locations are compared to criteria issued by the State of Colorado to determine if it's safe to be in contact with waters in Denver’s streams and lakes. 

  • The South Platte-Cherry Creek confluence (sampled weekly, May-October and twice a month the rest of the year);
  • Bear Creek at the picnic shelter in Bear Creek Park (sampled weekly May through October);
  • Sloans Lake (sampled every other week, May-October);
  • Westerly Creek near the playground in great Lawn Park (sampled once or twice a month from May to October);
  • Berkeley and Rocky Mountain Lakes (sampled monthly from May to October);
  • A number of other sites on the South Platte River and Cherry Creek are sampled monthly and sites on Bear Creek are sampled once a quarter year-round. 

Historic data from DDPHE’s stream sampling efforts can be found on the Denver Open Data Catalog (search for water quality data). Information about water quality in streams throughout the metro Denver area can be found in the South Platte Urban Waters Partnership’s Water Quality Assessment Tool

Notice:  Regardless of recent sampling results and posted advisories, people should always use caution when recreating in urban surface waters.

Water Quality Reports and Data

The DDPHE's Environmental Quality Division monitors the streams and lakes within the City and County boundaries. Streams are monitored year-round while lakes are typically sampled once per year during the summer. Results from stream monitoring are summarized in a story map. Lake monitoring results are summarized in one-page briefs that are generally updated biannually. Lake summaries are intended to provide a quick look at lake background/history, developing issues, pressing problems and management recommendations. 

The most recent versions of these reports are available by clicking on the links below. Additionally, data are available from the City's Open Data Catalog. Contact the Environmental Quality Division by calling 311 for lakes data or to get copies of older reports.

Public Advisories

From time to time, events will occur that require advisories be posted on City lakes or streams. Those advisories can be found on our Facebook page. Long-term public advisories are described below:

Fish Consumption

Do not consume largemouth bass from Berkeley and Rocky Mountain Lakes due to elevated levels of mercury in fish tissue. Eating fish contaminated with mercury, a pollutant which interferes with the brain and nervous system, can cause serious health problems, especially for pregnant women and small children. First posted March 2006. Re-assessed in 2015 – advisory was maintained. Consuming fish from other streams and lakes is not recommended.

Bluegreen Algae

Sloan’s Lake typically has high levels of bluegreen algae during summer months as dry, hot weather makes bluegreen algae blooms more likely. People and animals are cautioned to avoid contact with the water around the algae slicks, particularly near the marina, boat ramp, boat dock, and the shallow perimeter between the boat ramp and boat docks. These areas typically have higher concentrations of algae. Click on the Bluegreen Algae section below for more information on the causes and risks of exposure to bluegreen algae.

Invasive Species

New Zealand Mudsnails have been found in the South Platte River. The New Zealand Mudsnail is an invasive species which competes with native fish populations. People fishing in the South Platte River are advised to clean their waders prior to moving to a different location on the South Platte River or to another stream. Visit the Colorado Division of Wildlife's webpage for more information on the New Zealand Mudsnails and how to properly clean waders to prevent spread.

Bluegreen Algae

Bluegreen algae is a type of bacteria (cyanobacteria) that grows in still waters, mostly in lakes, ponds and wetlands. It can also be found in the backwaters of streams during dry periods when flows are low. Bluegreen algae thrives when the water is warm and enriched with nutrients (phosphorous and nitrogen), which are plentiful in urban waters. When environmental conditions are right, algae can grow quickly. Blooms become visible when they accumulate on the water surface and form algae slicks, often appearing as green paint.

Bluegreen algae can produce several toxins that can make people, pets and other animals sick. People can experience skin rashes and lesions when skin contacts the algae. Ingesting water can cause vomiting, diarrhea or liver failure in extreme cases. Animals that ingest the water can also experience these symptoms. 

If you or a pet come in contact with bluegreen algae, the algae should be washed off the skin or animal's coat thoroughly. If symptoms are being experienced, contact your physician or veterinarian immediately. 

Please contact the Environmental Quality Division with questions or concerns on bluegreen algae. The Environmental Quality Division can be reached by calling 311 (or 720-913-1311 from a mobile phone). 

Waterbody covered in bluegreen algae


E.coli in Denver

Keeping Denver's lakes and streams clean requires everyone’s help. Runoff carries oil, chemicals, pesticides, fertilizers, pet waste, debris and sediment directly into storm sewers, streams and lakes without treatment.

Residents can help by taking a few precautions and changing habits in small but noticeable ways. Every individual action adds up, and every individual can make a difference. 



    Other Topics

    Trash and Litter

    Trash is the most visible pollutant found in streams. In a typical year, the Mile High Flood Control District collects approximately 100 tons of trash from the streams in Denver. Studies conducted by DDPHE and The Greenway Foundation in 2012 found that the most common types of trash collected in the South Platte River were cigarette butts and packaging, food packaging, plastic bags, Styrofoam, paper and cardboard. Results of the studies are summarized in this presentation.

    Group of individuals picking litter out of a waterbody

    Dead or Dying Birds

    Over the past two decades, DDPHE staff have observed dead and dying birds in the City’s lakes. The observations occur in the hottest months of the year, typically between late June and September. Two possible causes for the dead and dying birds have been identified: Avian botulism and West Nile Virus.

    Avian botulism affects waterfowl and shorebirds that ingest a toxin which is commonly found in sediment at the bottom of lakes. Birds suspected of having avian botulism often have trouble holding their necks and heads up and may also appear to struggle to swim across the water. Unfortunately, death by drowning is often the end result. 

    City staff routinely monitor for potential signs of avian botulism during warmer weather and respond by removing bird carcasses and working with rescue organizations to help sick birds as quickly as possible. Sick birds stand a good chance of surviving when promptly treated by local bird rehabilitators. Leaving infected carcasses in and around the waterbody increases the spread of the disease. It's very important that all carcasses, birds and others, be removed.

    For more information, visit USGS – Avian Botulism

    West Nile virus is a disease transmitted by mosquitoes. Mosquitoes become infected after biting an infected bird and then may pass the virus on to other birds, humans or animals. Mosquitoes carry the highest amounts of virus in late August and September until the weather cools and mosquitoes die off. To most, West Nile virus symptoms in birds appear to be similar to those of avian botulism.

    For more information, go to CDC’s West Nile Virus web page.

    Please contact DDPHE by calling 311 if you see multiple sick or dead birds in your neighborhood.

    Mosquito Control

    Denver’s Mosquito Management Program uses an approach designed to reduce public health concerns and provide information and education to residents and businesses to help them keep mosquito populations at a safe level.

    Learn more about DDPHE's Mosquito Control Program.

    Fish Kills

    Fish kills are occasionally observed in Denver’s streams and lakes. A fish kill is a localized die-off of fish populations. There are many causes of fish kills, but oxygen depletion is the most common. Oxygen depletion may be caused by drought, algae blooms, overpopulation, a sustained increase in water temperature, or extended periods of ice cover on shallow lakes.  Other possible causes can include high or low pH values or viruses which are often specific to a particular fish species.

    If DDPHE is aware of a recent fish kill, information will be posted on “Recent Fish Kills in Denver Streams or Lakes" in the “Public Advisories” section of the web page.

    If you observe dead fish in any of Denver’s streams or lakes, please report them by calling 311. 

    River Redevelopment Plans

    In 2014, the City’s Department of Parks and Recreation began work on an ambitious plan to improve the parks along Denver’s river corridor. Since then, improvements have been made to Lakewood Gulch, at the confluence of Weir Gulch and the South Platte River, Johnson Habitat Park, a stretch of river between Overland Pond and Pasquinel's Landing, Globeville Landing, and Confluence Park.

    The City is also working with the US Army Corps of Engineers on a plan to re-envision parts of the South Platte River, Weir Gulch, and Harvard Gulch. More information about that project can be found on the Denver Waterways webpage.

    Improvements include features that will benefit water quality in the South Platte River. DDPHE is working with the Parks and Recreation design team on a number of issues related to the park improvement projects including conducting environmental site assessments, ensuring design features improve habitat and water quality, and incorporating education and outreach efforts related to water quality and recreation in urban waters. 

    For more information about the improvements, visit Parks and Recreation’s Master Planning web page.

    Volunteer Opportunities

    • Adopt a trail or a park or find volunteer opportunities on Denver’s Department of Parks and Recreation Volunteer page
    • Volunteer at one of The Greenway Foundation’s Riversweeps.
    • Check Groundwork Denver’s calendar of volunteer opportunities.
    • Organize a neighborhood stream or lake cleanup by contacting DDPHE.

    How You Can Help

    Here are things residents can do to help keep Denver's streams and lakes clean:

    • Take a pledge to protect Denver's lakes, streams and wetlands.
    • Dispose of garbage in a trash receptacle, not on the ground or in the gutter.
    • Pick up after pets and place the waste in a trash receptacle.
    • Apply fertilizer and pesticides in accordance with manufacturer's recommendations.
    • Don't apply fertilizer and pesticides before a storm.
    • Use phosphorus-free fertilizer.
    • Make sure vehicles are properly maintained to minimize leaks and drips.
    • Wash vehicles at a car wash, not in driveways or streets.
    • Dispose of household and hazardous chemicals (such as paint, pesticides or vehicle oil) properly. For information on disposal, visit Denver's Household Hazardous Waste Collection Program or call to schedule a pick up at 1-800-HHW-PKUP (800-449-7587).
    • Dispose of unwanted medicine and prescriptions at a medication take-back event. To find the next take back event near you or to find medication disposal locations, visit Take Meds Seriously’s Safe Disposal website.
    • Volunteer to adopt a trail or park near a steam or lake, or participate in an event like RiverSweep. To adopt visit Denver Parks and Recreation volunteer site, or volunteer at one of The Greenway Foundation and Groundwork Denver's river clean up events.
    • Report any of the following unusual conditions in Denver's lakes and streams by calling 311:
      • A change in color of the water
      • An unusual or foul odor
      • Suds when there has not been recent precipitation
      • Any unusual-looking substance discharging from a storm outlet
      • Illegal dumping activity
      • Unusual discharges from construction sites or industrial sites
      • A large number of dead or dying aquatic animals including fish, crayfish, insects, waterfowl or other animals