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Frequently Asked Questions
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Download the HAB brochure, available in English or Spanish.

Harmful Algae Bloom FAQs

Q: What is an algae bloom?

A: Algae are microscopic plants that grow naturally in oceans and fresh waters. Under certain conditions, some algae can grow into a large visible mass called a bloom.
Q: Why are algae blooms a health concern?

A: Not all blooms are harmful, but some species of algae, such as cyanobacteria or blue-green algae, can produce toxins or poisons that can cause serious illness or death in pets, livestock, wildlife and humans.
Q: How will I know if a toxic algae bloom is present? 

A: 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.
Q: What are the health risks posed by exposure to toxic algae? 

A: 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. 

Q: How can I protect myself when I am camping or recreating at a lake where a bloom is in process? 

A: Stay out of the affected water. Keep children and pets away. Never drink or cook with the affected water. If you touch the affected water, wash off thoroughly with another source of water.
Q: Can I treat algae-affected water to make it  safe? 

A: No. 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.
Q: Is it safe to eat fish? 

A: 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. Do not eat fish or crayfish harvested from affected waters.
Q: My drinking water comes from a water source that is affected by algae blooms. Am I at risk? 

A: People who draw water directly from an affected water body are advised that it may be dangerous to drink. If you or your drinking water supplier uses water from an affected source, call and ask if the water has been tested. If it has not been tested, it is recommended that you use an alternative water source not affected by the bloom. To learn more about harmful algae blooms and your drinking water visit the Oregon Health Authority Algae Resources for Drinking Water webpage.
Q: What about other outdoor activities? 

A: Camping, picnicking, hiking, biking, bird watching and other activities that do not involve water contact are encouraged. Boating is safe as long as speeds don't whip up excessive water spray, which could create an inhalation risk.


    Join Our Listserv

The HABS program has created a listserv to share information with partners, stakeholders and interested public. When a health advisory is issued, an email is sent to subscribers that includes the news release and water sample results (algae species and cell counts). Emails are also sent when an advisory is lifted. Other timely information may be periodically shared as well. To join the list, email us at