Department of Ecology News Release - September 14, 2011


Late summer at the lake? Watch for blue-green algae

SPOKANE – The Washington Department of Ecology (Ecology) is reminding residents of Eastern Washington who live on or near lakes or who visit lakes, to keep children and animals away from blooms of blue-green algae because they can be toxic.

When an algal species reproduces rapidly and reaches high concentrations, it is called an algae bloom. The algae blooms show up every year in many of our lakes and even rivers, often in late summer or early fall when the water is warm, sunshine is abundant and the weather is calm. However, they can occur at any time. Within only a few days, a clear lake can become cloudy.

The problem comes when a bloom produces toxins. Although many blue-green blooms are not toxic, some blue-green algae produce nerve or liver toxins. Toxicity is hard to predict since single species of algae can have both toxic and non-toxic strains.

Some dangerous kinds of algae produce a toxin that is found most often in the scum that people can see on top of the water. Only laboratory tests can confirm whether a bloom is toxic or non-toxic.

“Toxicity changes all the time, so water that’s perfectly safe may become toxic in just a few days, and vice versa,” said Mike Hepp, a water quality specialist in Ecology’s Eastern Regional Office in Spokane. “It’s unpredictable. People should stay away from it, kids should not be allowed to play in it, and livestock should be kept away from scummy water, too. Dogs should not be allowed to play in water that has a bloom and has not been tested.”

Here is what to look for: Blue-green algae cells are very small and they don’t clump together, although they can look like a mat. For this reason, they are hard to pick up or hold. In calm weather, the paint-like scum forms on the water surface. It can be either bright green or blue-green. (It is NOT stringy strands.) If the weather turns windy, the algae will be mixed in the water, making it look like pea soup. Blue-green blooms can float to the surface of the water and be several inches thick near the shoreline.

“It is usually scummy – something no one would want to swim in anyway,” Hepp said.

People and pets may become ill after contact with water such as swimming in lakes with toxic blue-green algae, according to the Washington State Department of Health. State health officials say, “When in doubt, stay out.”

Symptoms that people might experience include stomach pain, vomiting, diarrhea, and skin rashes. Exposure to nerve toxins can cause weakness, loss of muscle coordination, difficulty in swallowing, labored respiration, or tingling lips.

Toxic blue-green algae blooms also can hurt tourism and recreation, thereby having an effect on the economy of the region.

For more information on algae, visit Ecology's website (


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