Blue-Green Algae

*There are no Cyanobacteria advisories currently in effect for lakes on the Ochoco National Forest & Crooked River National Grassland. 

When there is a blue-green algae bloom present on an Ochoco National Forest or Crooked River National Grassland body of water, we will post these signs.

Algae are microscopic organisms that grow naturally in oceans and fresh waters. Under certain conditions, some algae can grow into a large visible mass called a bloom. Not all blooms are harmful, but some species of cyanobacteria, or blue-green algae, can produce toxins or poisons that can cause serious illness or death in pets, livestock, wildlife and humans.

Algae blooms appear as thick foam or scum on the water’s surface. They can be bright green, blue-green, white or brown in color. Unfortunately, you cannot tell if an algae bloom is toxic just by looking at it. If you come across areas of thick algae, take precaution by avoiding water contact and keeping pets out of the water.


Skin irritation or rash is the most commonly reported health effect. Other symptoms range from diarrhea, cramps and vomiting to fainting, numbness, dizziness, tingling and paralysis. The most severe reactions occur when large amounts of water are swallowed. The chronic effects of long-term exposure to algae toxins are being studied.


Stay out of the affected water. Keep children and pets away. Never drink or cook with the affected water. If you come in contact with the affected water, wash off thoroughly with another source of water.

Personal water filtration devices that may be purchased in outdoor recreational stores have not been proven to be effective. Boiling water will not remove the toxins. Fish caught in affected waters pose unknown health risks. If you choose to eat them, remove all fat, skin and organs before cooking because toxins are more likely to collect in these tissues.

For more information, visit the Oregon Health Authority website for Cyanobacteria or you can download this poster.