Prospect Lake remains closed as test returns positive for blue-green algae

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COLORADO SPRINGS, Colo. – Test results received Monday, June 22 confirm the presence of blue-green algae in Prospect Lake in Memorial Park. The lake was closed to bodily contact on June 15 following a visual inspection by Parks, Recreation and Cultural Services staff. The test, which drew a water sample on June 16, returned a mycrocystin level of 22 micrograms per liter. The acceptable recreational level for myrocystin, a toxin produced by cyanobacteria (also known as blue-green algae), is 4 micrograms per liter.

Test results will be published at

Prospect Lake was closed for 12 weeks in the late summer and early fall of 2019 due to blue-green algae. Since that time, Parks’ staff has taken proactive measures, including the application of an enzyme-based, non-pesticide treatment that consumes the biomass at the bottom of the lake and helps oxygenate the water. The first three treatments were applied May 26, June 11 and June 16.

The next scheduled treatment is Tuesday, June 23, and media are invited to capture footage of the application at 9:30 a.m. Media should park at the south end of the lake near the intersection of Union Boulevard and Prospect Lake Drive.

During the closure, the following activities are prohibited: swimming, bathing, paddle boarding, tubing, water skiing and non-motorized boating of any kind. No pets are allowed. The use of permitted motorized boats is encouraged as this activity can help aerate the water. Fishing areas will remain open, though anglers are urged to clean fish well and remove guts.


What is harmful algae? 

Blue-green algae are a type of bacteria common in lakes throughout Colorado. When conditions are right, blue-green 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 the harmful bacteria to grow faster than the ecosystem can handle. The increased bacteria harm water quality, decrease the amount of oxygen available to animals living in the water, and can produce a toxin that is harmful to humans and pets. 

Blue-green algae are self-limiting, naturally-occurring bacteria, which means it eventually phases itself out of bodies of water.

The Colorado Department of Public Health and Environment (CDPHE) offers additional information about blue-green algae on its website.

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