Toxic algae blooms, which the summer months bring, can kill pets, particularly dogs, the Colorado Department of Public Health and Environment warned on Thursday.

People recreating in Colorado waters should be aware that hot summer months are the peak period for toxic algae blooms in Colorado, the agency said in a news release.

While algae and cyanobacteria — the blue-green algae — are natural to Colorado’s water systems, they can overgrow in warm, nutrient-rich water, producing poisons that can harm people, animals, and the environment, the agency said, adding they cause skin irritation, diarrhea, stomach pain, fever, headache, and sore throat. For pets, they can be deadly.

“We want everyone to be able to safely enjoy the great outdoors in Colorado,” said Jill Hunsaker Ryan, the department’s executive director. “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.”

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

The agency said toxins had been detected at Cherry Creek Reservoir, but the bloom there has resolved. Blooms have also been reported at John Martin Reservoir, although testing did not detect any toxins. Meanwhile, a caution advisory was posted at Vega Reservoir on the Western Slope, and warnings have also been posted at Barr Lake and DeWeese Reservoir.

The healthy agency said people should stay out of the water if they see these conditions:

• 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 
• Has foam, scum, or algae mats
• Has dead fish or other animals washed up on its shore or beach

The agency recommends rinsing with tap water any portion that comes into contact with toxic algae and ensuring pets don’t lick their fur until after they have been thoroughly rinsed. Pet owners should immediately contact a vet if they experience symptoms, and people can also contact poison control at 1-800-222-1222, the agency said. 

People can help minimize algae blooms by picking up and properly disposing of pet waste, refraining from using too much fertilizer, and avoiding de-icers that contain urea.