Blue-Green Algae and Health Impacts
Be cautious of algal blooms in lakes and ponds. Boulder County does not test for toxic algae.
Blue-green algae has been confirmed in lakes and ponds in Colorado for the past few years, but Boulder County Public Health does not test for it in any parks and open space areas.
Not all algae is harmful to humans or pets, but the best way to keep your family safe during an algae bloom is to:
- Keep out of the water, including children and pets.
- Avoid drinking the water. Ingestion of blue-green algae can cause gastrointestinal distress in humans and is potentially lethal to dogs.
- Avoid boating near or through algae blooms.
- Clean fish well and discard the guts appropriately.
- When in doubt, stay out!
Blue-Green Algae
Some algal blooms can contain cyanobacteria, often referred to as blue-green algae. While the vast majority of algae often seen in ponds and lakes during summer months are not toxic, cyanobacteria can produce toxins, which can be harmful to dogs and humans at elevated levels. Warmer temperatures, stagnant water, and nitrogen and phosphorus (nutrient) loading from fertilized lawns and other sources can facilitate algae and cyanobacteria growth.
According to the Colorado Department of Public Health and Environment, cyanobacteria blooms may look like thick pea soup or spilled bluish-green paint on the water’s surface. They can also create a dense mat of foam along the shoreline. The long, stringy, bright green strands that appear slimy or cottony or mustard yellow are not harmful types of algae.
At lakes and ponds where dogs are allowed to enter the water, exercise caution if algae is present. Anglers should also exercise caution and follow state recommendations to clean any caught fish thoroughly and discard guts appropriately.
Visitors and residents should exercise caution and keep children and pets out of the water in any areas where algae are observed. When in doubt, stay out.
