COLORADO SPRINGS — The Colorado Department of Public Health and Environment (CDPHE) reminds people recreating in Colorado waters to be aware of toxic algae blooms during the hottest summer months.

DeWeese Reservoir photo of algae that tested positive for toxins Taken June 22, 2022

Algae and cyanobacteria (sometimes called blue-green algae) are natural to waters in Colorado but can overgrow or bloom in warm, nutrient-rich water. Toxic algae occur if the blooms produce poisons that can harm people, animals and environment.

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

When exposed to Toxic algae, it can cause a variety of symptoms in people, including skin irritation, diarrhea, stomach pain, fever, headache, and sore throat. CDPHE says that 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.”

For 2022, CDPHE added a “recent conditions” map to its toxic algae dashboard. This new map provides more up-to-date information about toxic algae blooms around the state and is updated each week. Ssince bloom conditions change rapidly, the state recommends that people consult the waterbody managing agency website before visiting a body of water.

“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.”

Only lab tests or test strips can determine if an algae bloom is toxic, according to CDPHE. However, you can look for certain characteristics that are common among toxic algae:

  • Has a bad odor.
  • 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 1-800-222-1222.

State testing for the summer of 2022 has detected toxins at Cherry Creek Reservoir, but the bloom has since been resolved. Blooms have also been reported at John Martin Reservoir but continued testing has not detected any toxins. A caution advisory has been posted at Vega Reservoir on the Western Slope, and warnings have been posted at Barr Lake and DeWeese Reservoir.

People also have a role to play in preventing toxic algae, says CDPHE. 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.