Test Results Show High Levels of Toxic Algae in Prospect Lake

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More testing of water in Prospect Lake shows high levels of microcystin, which can be produced by blue-green algae. The toxin is dangerous to people and animals.

The Parks, Recreation, and Cultural Services Department closed the lake Friday, Aug. 9, after a preliminary test by the Colorado Department of Public Health and Environment (CDPHE) returned positive for microcystin. Results received later that evening from a more precise test showed a microcystin level of 29.7 mcg/L, well above the state’s closure level for recreation, which is 4 mcg/L.

Date Tested

Date Results Received

Microcystin level

Testing Agency




Colorado Springs Utilities



29.7 mcg/L

Colorado Department of Public Health & Environment



Present (<5 ppb)

Colorado Department of Public Health & Environment

8/13/2019 8/15/2019 20.9 mcg/L Colorado Department of Public Health & Environment
8/20/2019 8/22/2019 91 mcg/L Colorado Department of Public Health & Environment

The Colorado Department of Public Health and Environment will continue to test the lake weekly until it's determined to be safe.

Parks staff have posted signs throughout the park and along the shoreline. It's important for everyone to follow the posted information. Stay out of the water even if you don't see any algae.

The following activities are not allowed: swimming, bathing, paddle boarding, boating of any kind, water activities like tubing and water skiing. Pets are not allowed in the water.

Fishing areas will remain open, anglers should clean fish well and remove guts.

This "algae bloom" is naturally occurring. The algae levels will decline as part of the natural process. How long that will take it hard to determine. For updates go to the Memorial Park Page.

Blue-green algae are a type of bacteria common in lakes throughout Colorado. When conditions are right, the algae multiplies quickly. Those conditions include sustained hot weather, stagnant water, and polluted stormwater runoff.

These conditions result in too much nitrogen, potassium and phosphorus in the water. This causes algae to grow faster than the ecosystem can handle. The increased algae harms water quality. It also decreases the amount of oxygen available to animals living in the water.

Additional Information