Colorado Springs officials confirmed the presence of blue-green algae in Prospect Lake Monday and continued the lake's closure indefinitely.

Parks staff closed the lake to swimmers, boaters and anyone else who could come into contact with the water June 15 after noticing a change in the water's color. Staff subsequently took a water sample, which showed a mycrocystin level of 22 micrograms per liter, city officials said Monday. The acceptable recreational level for myrocystin is 4 micrograms per liter.

The bacteria is a toxin produced by cyanobacteria (also known as blue-green algae) that harms water quality, decreases the amount of oxygen available to animals living in the water, and can be toxic to humans and pets. Steady hot weather, polluted stormwater runoff, and stagnant water create ideal conditions for the algae to multiply.

Fishing piers remain open, but anglers are encouraged to clean their fish well. 

Prospect Lake was closed for 12 weeks in the late summer and early fall of 2019 because of the blue-green algae. Since then, city officials have applied 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 at 9:30 a.m.

To see the latest test results, visit



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