Blue-Green Algae Information

What is a blue-green algae bloom?

Blue-green algae are bacteria that have qualities like algae and other plants.  These bacteria are cyanobacteria - cyan means "blue green" - and are commonly found on land and in lakes, rivers, ponds, or other bodies of contained water.

Warm temperatures, sunlight and slow-moving or stagnant waters with lots of nutrients can accelerate the growth or “bloom” of blue-green algae. Within days, a clear body of water can be covered with it. Although these algae can be annoying and impact water quality, it’s often non-toxic. However, some can produce toxins that can cause illness in humans, pets and other animals. In some cases, toxic blooms can kill livestock and pets that drink the water.

A blue-green algae bloom:

  • Often looks like green paint floating on the water, but can look bluish, brownish, or reddish green.
  • Can be several inches thick around the shoreline.
  • Is hard to pick up or hold because of how small the individual “blooms” are.
  • Is most common in the summer and fall but can occur anytime.

Signs of a toxic bloom may include:

  • Dead fish, waterfowl, or other animals.
  • Sudden, unexplained sickness or death of a cat or dog, especially if it has algae on its mouth, legs, or feet.
  • Skin rashes on humans after being in the water. 

Eventually the toxins break down in the water and are destroyed naturally.

What if I see a bloom?

If you see a bloom, you, your family and your pets should avoid contact with the water and call the Chelan-Douglas Health District’s Environmental Health Office at (509) 886-6400. If you see a bloom, or suspected bloom at a Chelan County PUD managed shoreline please contact us at (509) 663-8121.

photo of a blue green algae bloom

For more information on blue-green algae, please visit:

Chelan-Douglas Health District  (English and Spanish options) 

Department of Ecology Freshwater Algae Control Program

Washington State Toxic Algae (The website includes statewide data and map of testing sites)

For more information in Spanish visit Washington State Toxic Algae (nwtoxicalgae.org).