Algae reappears in Johnston Reservoir

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By Ramsey Scott

The blue-green algae that caused the Johnston Reservoir at Clement Park to close last summer is making an appearance again. 

The algae, also known as cyanobacteria, can produce toxins harmful to humans and animals. Last August, the algae became so pervasive that the Jeffco Public Health Department prohibited wading, fishing or contact with water in the reservoir. 

The Foothills Park & Recreation District recently found the algae blooms.

“If it gets worse and the water is deemed to be unsafe for contact, we’d have to close it again,” said Ron Hopp, Foothills executive director. 

Hopp said warm weather plus a lack of moisture causes the algae to form, especially in the northwest corner of the reservoir where the water is shallow. 

“It’s really caused by the heat and organic matter in the water that basically ferments, for lack of a better term, and it causes the bacteria to form,” Hopp said. 

Hopp said after the health department closed the reservoir last year, Foothills looked into finding a solution to the problem, and all of the proposed remedies are cost prohibitive. 

One remedy would be to install an aeration system to help circulate the water and prevent algae from forming at a cost of several hundred thousand dollars, Hopp said.  

“We also got estimates and proposals from some companies that do water treatment and quality, and it was a similar number with no guarantees of long-term benefits,” Hopp said. 

While the reservoir isn’t experiencing algae levels this year that compare with the massive amount that covered most of the reservoir last year, Hopp said Foothills will monitor the situation closely and will contact the health department.

“It depends on the weather whether it will get worse or better,” Hopp said. “We’ll hope for some cooler weather.”


 Contact Ramsey Scott at ramsey@evergreenco.com or 303-933-2233, ext. 22 and follow him on Twitter @RamseyColumbine.