Water Quality Program

Welcome to the home of DEH’s Water Quality Program!

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

Water Quality in Lakes and Streams

Denver’s goal is to have fishable and swimmable waters in all our lakes and streams by 2020. Denver’s Departments of Environmental Health, Public Works, 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:

  • The City has developed a program to improve storm water facilities in 10 priority areas with the intent of protecting water quality in the river. To date, the program has successfully reduced the amount of bacteria entering the South Platte River from most of the basins. It is still too soon to tell how those reductions have affected water quality in the South Platte River.
  • The Department of Public Works recently rewrote its rules and regulations to ensure that development and redevelopment projects in the City are designed to treat for water quality on site.
  • The City is identifying areas where more facilities are needed to ensure storm water runoff is adequately treated to remove sediment, trash, and other pollutants.  City staff are using this information to develop a plan to add water quality treatment facilities in those areas.

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 you sick.

DEH does not recommend swimming, wading, or playing in City streams or lakes. Swimmers are encouraged to use the swimming facilities provided by the Denver Parks and Recreation Department 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 tips to help keep you safe:

  • 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.
  • Avoid waters near flowing storm drains
    • Water coming out of storm drains may contain bacteria or other pollutants that can make you sick.
  • Avoid areas where the water is not flowing
    • The lack of flow allows bacteria to accumulate to levels that can make you sick.
  • Avoid areas with trash and other signs of pollution such as oil slicks or scum
    • These signs may indicate the presence of disease causing microorganisms.

Denver Water Quality employee sampling water at Sloan's LakeDEH samples most of the streams and many of the lakes in Denver at least once a year. Sampling results 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. DEH posts information on the latest water quality results for the following sites on the map below and on our Facebook page. The map includes photographs of many of the sampling locations.

  • 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);
  • Cherry Creek near Garland Park (sampled twice a month from May to October and the rest of the year);
  • 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. 

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

The Denver Department of Environmental Health’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 monitoring are summarized in annual reports.

The most recent versions of our reports are available by clicking on the links below. For additional information or to get copies of older reports, please contact the City and County of Denver by calling 3-1-1 and requesting the Division of Environmental Quality.

From time to time events will occur that require advisories be posted on City lakes or streams.  Information about those advisories can be found here.


  • There are no reports of spills at this time.


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. 


Fish Kills

  • As of February 2nd, 2015, DEH is aware of recent fish die offs in three lakes in Denver: Aqua Golf Lake near east of Overland Park, Lollipop Pond Lake in Garland Park, and Smith Lake in Washington Park.  The fish kills were observed after the ice had begun receding on January 30th.  The fish deaths are likely a result of a phenomenon known as winter kill in which lakes freeze over during cold weather and dissolved oxygen is consumed by decaying organic matter in on the lake bottom.  The amount of oxygen used up in the decay process is higher than the amount of oxygen produced by algae. This can result in lethal conditions for fish when there is prolonged snow cover on the ice which limits sunshine penetration necessary for algae to photosynthesize (produce oxygen). If you observe fish kills on other lakes in Denver, please report it to 3-1-1. 


  • There are no other advisories at this time.

Other Topics

Trash is the most visible pollutant found in our streams. In a typical year, the Urban Drainage and Flood Control District collects around 100 tons of trash from the streams in Denver.

In 2012, the City’s Environmental Health and Parks and Recreation Departments partnered with The Greenway Foundation and several other organizations to address trash in the City’s streams. The goal of the partnership is to collect information about the types and extent of trash in Denver’s streams and to understand people’s knowledge and attitudes towards littering.

Efforts to understand the types and extent of trash began with trash inventory and clean up events on the South Platte River in 2012. The inventories consisted of collecting and categorizing trash at several locations along the banks of the South Platte River and bagging it for proper disposal. The most common types of trash collected were cigarette butts and packaging, food packaging, plastic bags, Styrofoam, and paper and cardboard. See a Summary of the results. A follow up survey was conducted on Cherry Creek in 2014. The results of the survey were similar to the results from the South Platte River.

The project team also conducted telephone surveys to gauge the public’s understanding of trash in streams and attitudes towards littering. The surveys identified a number of areas where knowledge and attitudes towards littering could be improved.

Information from the study was used to develop an information and education plan which is intended to change people’s attitudes and behaviors towards littering.

In 2015, DEH will begin planning one of the more important pieces of the information and education plan - a River Summit, to be held in 2016. The River Summit will be an opportunity for Denver residents to let the City know what their priorities for the City’s streams and lakes are.  

Over the past decade, DEH 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 sediments 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 such as Wild B.I.R.D. or the Denver Zoo.

West Nile virus is a potentially serious disease which is 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 the early fall, but the risk of disease decreases as the weather becomes colder and mosquitoes die off.  To most people, the symptoms are similar to those of avian botulism.  Please contact Denver Environmental Health (by calling 3-1-1) if you see multiple sick or dead birds in your neighborhood.

Click here to learn about DEH's Mosquito Control Program.

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 cause. Oxygen depletion may be due to factors such as drought, algae blooms, overpopulation, a sustained increase in water temperature, or extended periods of ice cover on shallow lakes.

If we are aware of a recent fish kill, we will post information on recent fish kills in Denver streams or lakes in the Public Advisories section of our web page.

If you observe dead fish in any of Denver’s streams or lakes, please report them by calling 3-1-1. 

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. Improvements at the confluence of Weir Gulch and the South Platte River were completed and work to improve Johnson Habitat Park and Overland Park started. In addition, the City began raising funds for the first phase of improvements at Confluence Park. Plans for these parks include features that will improve water quality in the South Platte River. DEH is working with the Parks design team on a number of issues related to the park improvement projects including environmental site assessments, ensuring design features improve habitat and water quality, and incorporation of education and outreach efforts related to water quality and recreation in urban waters.  

The City’s Department of Parks and Recreation has plans for improvements at many other parks along streams and lakes in Denver. For more details, visit Parks and Recreation’s Master Planning web page. More information on the River visioning process, including planning documents can be found on The Greenway Foundation’s Website.

Concept for improvements to the boat launch at Johnson-Habitat Park. Used by permission of Denver Department of Parks and Recreation.

How Can I Improve Water Quality?

Keeping Denver's lakes and streams clean requires everyone’s help. Runoff carries with it oil, chemicals, pesticides, fertilizers, pet waste, debris and sediment directly into the storm sewer, stream, or lake without treatment.

You 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.

Volunteer Opportunities

Here are a couple of places were you can find out about opportunities to help Denver keeps its lakes and streams clean:

  • Denver’s Department of Parks and Recreation keeps a list of volunteer opportunities on their web page
  • DEH’s Water Quality Program occasionally posts volunteer opportunities on our Facebook Page.


  • Tie the bag up securely and place it in the garbage.


  • Trash on the ground ends up as trash in streams and lakes.


  • Over-application of fertilizer and pesticide contributes to overgrown algae and weeds in lakes and streams. Fertilizer and pesticides are also toxic to pets, other animals, and even people.
  • Dispose of excess pesticides using the City of Denver's Household Hazardous Waste Collection Program. Call 1-800-HHW-PKUP (1-800-449-7587).


  • Oil, gas, coolants, and other automotive fluids can pollute Denver’s streams and lakes. As little as four quarts of oil dumped down the storm sewer can create an eight-acre oil slick! Regular maintenance can prevent drips and leaks from your car which can pollute our streams.


  • Excess watering not only wastes water, it increases runoff of fertilizers and pesticides into the storm sewer. Information on how to conserve water, including how often to water plants and the best time of day to water, can be found on Denver Water’s website.


  • Soaps and detergents contain chemicals which can reduce oxygen in lakes and streams.
  • Wastewater from commercial car washes is treated before discharge to area streams or lakes.


  • See the Household Hazardous Waste (HHW) Collection Program Number above.


  • Be a watchdog over our lakes and streams. Contact 3-1-1 if you notice any unusual conditions in our lakes and streams.

Water Quality Map

How to use this map:

Icons are located at water sampling areas. A red icon indicates that the site is not safe for recreation. Clicking on the icon will open up a window with a photo of the area, a description of the site, and information related to the most recent sampling results.