WESTCLIFFE, Colo. – A growing bloom of toxic blue-green algae at DeWeese Reservoir State Wildlife Area has prompted Colorado Parks and Wildlife to warn the public to avoid contact with the water.

“Algae has become a seasonal problem at DeWeese, forcing CPW in recent summers to close the water to all activity except fishing to prevent the risk of exposure to humans and their pets,” said CPW District Wildlife Manager Justin Krall. “The algae can be harmful to people and pets if touched. It can give sensitive people a bad rash, for example. And it’s possibly fatal if ingested.”

Signs are being posted at the reservoir by CPW warning visitors to avoid the water and explaining the danger of the algae blooms, saying:

  • Do not drink the water
  • Do not recreate in the water (including swimming, skiing, paddle-boarding, and wading)

If anyone or their pet comes into contact with the algae, signs urge them to shower immediately with fresh, clean water.

The warning was prompted after testing found dangerous levels of toxicity in the water and elevated levels of algae were observed in a turquoise-colored film on the reservoir. 

“You can still fish during an algae bloom,” Krall said. “But there should be no skin-to-water contact.

“It’s also important to take care when handling and cleaning any fish caught in DeWeese. Toxins accumulate in the liver and guts of fish. So it’s important any fish taken is properly cleaned and thoroughly cooked before eating it.” 

Algae blooms are common when temperatures rise, usually in late summer, he said. CPW has been monitoring the reservoir closely, taking weekly water samples to check for elevated toxicity.

Other forms of recreation still allowed at the SWA include: picnicking, hiking, wildlife viewing and camping.  

Algae are an important part of aquatic food webs, but some types of blue-green algae are capable of producing toxins that may cause negative health impacts for humans and pets at elevated concentrations. Currently there is no method to remove toxins from lakes.

More information on blue-green algae is available on CDPHE’s website.

The public can help reduce the occurrence of blue-green algae blooms by preventing nutrients (nitrogen and phosphorus) from entering waterways through responsible use of lawn fertilizers, picking up pet waste, and avoiding using deicers that contain urea.