About algae blooms

Blue-green algae are common

Blue-green algae are a kind of bacteria common in Colorado waters. Water nutrients such as nitrogen and phosphorus help algae grow and support fish and other aquatic life.  But too much nitrogen and phosphorus in the water allows blue-green algae to grow quickly and form blooms and scums. Blooms can occur anytime but are most common during hot, sunny weather and in slow-moving water bodies such as lakes. Some algae blooms produce toxins (poisons) that can cause illness in humans, pets, waterfowl, and other animals that come in contact with the algae. These are called harmful algae blooms (also called HABs or toxic algae). 

Harmful algae blooms in Colorado

Harmful algae blooms happen frequently in Colorado, particularly during warm months. They may occur anywhere but are less likely in high-elevation mountain lakes and reservoirs. The only way to know if an algae bloom is harmful is to have it tested.  The Colorado state lab is one lab that can run these tests.

Harmful algae blooms

  • May look like thick pea soup or spilled paint on the water's surface.
  • Can create a thick mat of foam along the shoreline.
  • Usually are green or blue-green, although they can be brown, purple or white.
  • Sometimes are made up of small specks or blobs floating just at or below the water's surface.  

Harmful algae blooms are not

  • Long, stringy bright green grass strands that feel either slimy or cottony.
  • Mustard yellow (this probably is pollen).