July 7, 2022

As Temperatures Heat Up Watch for Harmful Cyanobacteria Blooms when Recreating

Press Release from U.S. Forest Service, Arapaho and Roosevelt National Forests 

In the wake of the East Troublesome Fire, a coalition of agencies is collaborating to protect public health and safety in Grand County’s Three Lakes Region. Wildfires can create numerous issues for waterways, from flooding and sedimentation to nutrient runoff that can lead to Harmful Cyanobacteria Blooms. 

Northern Water, Grand County, the Arapaho National Forest, Bureau of Reclamation, the Grand County Water Information Network, the Town of Grand Lake, and Colorado Department of Health and Environment have spent the past year creating a comprehensive plan for monitoring and responding to Harmful Cyanobacteria Blooms in the Three Lakes region. 

Public education is an important first step to preparing for the possibility of Harmful Cyanobacteria Blooms. Cyanobacteria blooms can occur under certain environmental conditions that promote intense growth. These conditions include high temperatures, still water conditions, and increases in nutrients, common after a wildfire. In some cases, the cyanobacteria blooms have the potential to become toxic and can cause harm to humans and animals that come into contact or ingest the water. These cyanobacteria blooms are called Harmful Cyanobacteria Blooms but Harmful Algal Blooms, Blue-Green Algae, and Toxic Algae are also common terms.

Grand County Cyanobacteria Monitoring and Outreach

Recreational use health advisory warnings will be issued if people need to stay out of affected waters to avoid illness. This will occur if a cyanobacteria bloom is found and lab results show cyanotoxin levels over Colorado Department of Public Health and Environment’s and the EPA’s recreational use advisory levels.  

Recreational use health advisories are posted at primary access points and shared on the Grand County website: www.co.grand.co.us/HCB.   


Exposure to cyanotoxins can be serious and result in a range of symptoms. This includes: 

  • Diarrhea 
  • Cramps 
  • Vomiting 
  • Numbness 
  • Dizziness 
  • Fainting 

Contact with a bloom can cause a puffy, red rash. Children and people with weakened immune systems are most vulnerable to illness. 

Pets are at risk, too

Due to their size and activity level, dogs are very vulnerable to the effects of cyanotoxins. Dogs can be exposed through: 

  • Drinking affected water 
  • Eating cells from the bloom 
  • Licking cells off rocks, and 
  • Licking their fur after exposure 

Symptoms can occur very quickly and owners of dogs exhibiting abnormal behavior after being in the water should call a veterinarian immediately. 

When to avoid water contact

Because only a fraction of Grand County’s fresh waters is visually monitored and sampled, the public can’t be notified about all harmful cyanobacterial blooms. Therefore, the public should look for certain conditions before entering the water to stay safe and healthy. It is best to stay out of an area if the water smells bad or looks: 

  • Foamy, scummy, thick like paint, and 
  • Pea-green, blue-green, or brownish-red in color 

Local agencies will alert the public about blooms and cyanotoxins to protect public health. For more information and resources on reporting a potential bloom, please visit www.co.grand.co.us/HCB.