CPW warns public to avoid toxic algae bloom in DeWeese Reservoir

Dean Miller
Southeast Region Public Information Officer
719-466-3927
[email protected]

Aug. 20, 2025

WESTCLIFFE, Colo. – A growing bloom of toxic blue-green algae at DeWeese Reservoir State Wildlife Area prompted Colorado Parks and Wildlife to warn the public Aug. 19 to avoid contact with the water at that location for the first time this summer.

“Algae has become a seasonal problem at DeWeese, forcing CPW to alert the public in recent summers of dangers 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 posted at the reservoir by CPW warning visitors to avoid the water and explaining the danger of the algae blooms.

The signs warn people to keep kids and pets out of the water and to not drink the water at the risk of death from the toxic algae. The signs also state that the area is closed to water recreation including swimming, skiing, paddle-boarding, nor wading is allowed. 

If a person or their pet comes into contact with the algae, the 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 with precautions,” Krall said. “But there should be no skin-to-water contact.

“It’s 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 that 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.

DeWeese Reservoir SWA is a 300-surface-acre reservoir near Westcliffe with popular fishing. 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.

The Colorado Department of Public Health and Environment (CDPHE) recommends the following:

• Keep kids out
• No pets in water
• Do not drink water
• Avoid contact with algae
• If exposed, shower immediately

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 the use of deicers that contain urea. 

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PHOTO CUTLINES:

SIGN WITH RESERVOIR - A sign near the water warns the public to avoid the toxic algae bloom in DeWeese Reservoir State Wildlife Area. Lab tests confirmed the dangerous levels on Tuesday. DeWeese is a 300-surface-acre reservoir near Westcliffe. Picnicking, hiking, wildlife viewing and camping are still allowed. Fishing, in accordance with recommended safety precautions, is also still allowed. 

SIGN - A close-up of one of the many signs posted in DeWeese Reservoir State Wildlife Area warns the public to avoid the toxic algae bloom. 

ALGAE - The blue-green algae bloom at DeWeese Reservoir State Wildlife Area that prompted officials to conduct immediate field testing and lab verification. Testing confirmed toxicity levels requiring a recommended end to all water recreation beyond fishing. Fishing continues with recommended precautions.