There’s a toxic blue-green algae bloom at Cherry Creek Reservoir

Don’t go in the water.
2 min. read
Several large bunches of algae in shallow blue water just off a rocky shoreline. There's a small marina filled with boats in the background.
Algae on the shoreline at the Cherry Creek Reservoir.
Colorado Parks and Wildlife

Blue-green algae is blooming across the lake and shoreline at Cherry Creek State Park, and state officials recently warned visitors to stay out of the water.

In a social media post, the park advised visitors to keep children and pets out of the water. Boating and fishing are still allowed, but fishers should rinse fish and dispose of their guts before consuming.

According to the Colorado Department of Public Health and Environment, toxic blue-green algae occurs naturally in Colorado waters. But it can rapidly multiply and become a “bloom.”

The Centers for Disease Control and Prevention says this excessive growth can be caused by nutrient pollution in the water from fertilizers, sewage and “run-off from cities and industrial buildings.”

Warmer temperatures, low water levels and changes in the water’s pH help algae growth too.

These blooms release toxins that can irritate skin and cause headaches, muscle and joint pain, gastrointestinal issues and even liver damage.

Toxic green-algae blooms can look like thick pea soup or spilled paint on the water’s surface, so be on the lookout for these signs.

Cherry Creek State Park officials advised anyone who comes in contact with the algae to shower immediately. CDPHE also recommends seeking medical or veterinary care if visitors or their pets experience any symptoms.

CDPHE has a map tracking recent reports of toxic algae blooms across the state every summer, with selected lakes getting tested once a month. It lists a “caution” status for Cherry Creek Reservoir. Barr Lake, in Brighton, is under a more severe “warning” status.

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