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SLOAN’S LAKE, Colo. (KDVR) — For the first time ever, Sloan’s Lake is temporarily closed to the public because of deadly blue-green algae.

Scott Gilmore, with Denver Park and Recreation, tells FOX31 a combination of shallow waters, extreme heat and a lack of rain contributed to the ultra-high levels of cyanobacteria, also known as blue-green algae.

“We have to make decisions like this sometimes that are tough for the public to hear, but they are the decisions we have to make to manage the park safely,” Gilmore said.

Blue-green algae on Sloans Lake on Thursday, July 22, 2021.

Contact with the water and all recreational activities are prohibited, including fishing, wading, boating and use of hand launched or non-motorized craft such as canoes, paddleboards and kayaks.

Park visitors should not allow their children or pets in or near the water.

Blue-green algae is found naturally in all types of water, but this type of algae can poison dogs, cats, livestock, wildlife, birds, fish and humans. Pets can die within hours of consuming the algae.

According to Gilmore, people can get sick and experience symptoms including a headache, diarrhea, weakness and liver damage.

“We will not open the lake until we are sure the toxicity levels are down to a safe point,” said Gilmore.

Officials will continue to test algae levels throughout the summer and will reopen the lake when enough algae dies off, although that could take several months.

The annual Dragon Boat Festival should still take place this fall, but boaters will have to find a different city lake to practice in.

If you or your pets are exposed to the water and experience any of these symptoms, contact your doctor or veterinarian.