State urges Coloradans to be aware, avoid toxic algae


Colorado Department of Public Health and Environment

The Colorado Department of Public Health and Environment (CDPHE) reminds people recreating in Colorado waters to be aware that hot summer months are the peak months for toxic algae blooms in Colorado. 

Algae and cyanobacteria (sometimes called blue-green algae) are natural to our waters in Colorado, but can overgrow or bloom in warm, nutrient-rich water. Toxic algae occurs if the blooms produce poisons that can harm people, animals and the environment. Toxic algae can cause a variety of symptoms in people, including skin irritation, diarrhea, stomach pain, fever, headache and sore throat. Toxic algae can kill pets, especially dogs. 

 “We want everyone to be able to safely enjoy the great outdoors in Colorado,” said Executive Director Jill Hunsaker Ryan. “We are raising awareness about toxic algae so that people can be sure the waters they and their furry friends are playing in are safe.”

 This year, the CDPHE added a “recent conditions” map to its toxic algae dashboard. This new map provides more up-to-date information about toxic algae blooms. This information is updated each week. However, since bloom conditions can change rapidly, the state recommends people consult the waterbody managing agency website (if available) before visiting a waterbody, obey all signs and stay out of the water if they suspect toxic algae. 

“If you think an algae bloom might be toxic, keep kids and animals away from the water — when in doubt, stay out,” said Kristy Richardson, state toxicologist. “People can visit our dashboard, contact waterbody managers, look for posted signs, and follow simple steps to stay safe.”

Look for signs or other advisories from local public health authorities or waterbody managers. If a beach is closed, or if there is guidance to avoid the water, stay out and keep pets out. Only lab tests or test strips can determine if an algae bloom is toxic, but algae that may contain toxins has certain characteristics. Stay out of water that:

• Smells bad.

• Resembles thick pea soup or spilled paint on the water’s surface.

• Looks discolored — generally green, red, gold or turquoise, but typically not stringy or mustard yellow in color (the latter is probably pollen).

• Has foam, scum or algae mats.

• Has dead fish or other animals washed up on its shore or beach.

People and pets who come into contact with water that has toxic algae should rinse with tap water as soon as possible. Don’t let pets lick their fur until after they have been thoroughly rinsed. Contact a health care provider or veterinarian if you see any symptoms that are concerning. People also can contact poison control at (800) 222-1222.

Excess nutrients, high temperatures and standing or slow-moving water provide an optimal environment for toxic algae, so it’s not commonly found in rivers or high mountain lakes; however, toxic algae blooms at lower elevations are expected throughout the summer. 

People also have a role to play in preventing toxic algae. Pick up and properly dispose of pet waste, refrain from using too much fertilizer and don’t use de-icers that contain urea. These simple steps reduce the amount of nutrients entering the waterways, ultimately reducing the number and frequency of toxic algae blooms. 

More information is available at