Prospect Lake in Memorial Park reopened for recreation Tuesday after about a two-week closure because of dangerous levels of toxic blue-green algae, according to a news release from city officials.

The reopening comes after two consecutive negative tests “for an elevated concentration of blue-green algae,” the release stated.

Swimming, paddle boarding, tubing, water skiing, and non-motorized and motorized boating are now permitted.

A visual inspection by Parks, Recreation and Cultural Services staff alongside a water sample test by Colorado Springs Utilities led to the July 24 closure. Testing confirmed the presence of the mycrocystin toxin, produced by cyanobacteria, more commonly known as blue-green algae.

Blue-green algae is a type of bacteria common in lakes throughout Colorado. It multiplies quickly, especially when conditions are right, such as hot weather, stagnant water and polluted stormwater runoff.

The release warned that algae blooms remain possible through the end of summer because of warmer temperatures. Visitors are encouraged by the city to use caution by not drinking the water, keeping children and pets out of the water, and avoiding any contact with algae that may be present.

Fishing is permitted but anglers need to rinse fish with clean water and properly dispose of organs when processing. Boaters must also avoid any visible algae contact.

City parks staff will continue to monitor and perform weekly testing to ensure safe, recreational water quality levels set by the Colorado Department of Public Health and Environment and the Environmental Protection Agency.

A similar algae bloom closed the lake in 2020 and spawned a discussion of a permanent form of mitigation. City sources told The Gazette last month that the city is finalizing a contract and scope of work with Colorado Springs-based Timberline Building Systems to install the new permanent, continuous aeration system to control the algae.