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When in Doubt, Stay Out!

Cyanobacteria (Harmful Algae) Blooms

algae bloom

The Oregon Health Authority (OHA) collects and reviews available information on cyanobacteria blooms, and informs the public through the issuing and lifting of recreational use health advisories when water sampling data warrants.

This information allows people to take protective action to avoid illness before deciding where to recreate. OHA relies on water sampling data provided by our partners. Read more about the water sampling process.

View Current Advisories FAQs 

Report a HAB Report a HAB-Related Animal Illness Report a HAB-Related Human Illness


Benthic Cyanobacteria and Cyanotoxins

The science surrounding benthic cyanobacteria, the mats they form and the toxins they produce is ongoing. These cyanobacteria mats are found in clear water rivers and lakes and do not form the kind of scum people are used to seeing. Unlike planktonic species (those that are present in the water column), these cyanobacteria grow up from the sediment (river or lake bed), attach to rocks, and often grow on and within green algae. Mats are harder for people to identify than those that form scum or a bloom on the surface of the water, so knowing what mats look like, how they differ from surface water blooms and how you can avoid them will help to reduce you and your pets potential exposure to the cyanotoxins they often produce. For additional information about cyanobacteria blooms and benthic mats, OHA recommends watching the Interstate Technology and Regulatory Council's (ITRC) YouTube video "Learn to Identify Cyanobacteria Blooms". 

Cyanobacteria Bloom Awareness: You and Your Pet

Since most waterbodies in Oregon are not monitored, OHA staff recommend you become familiar with your surroundings and know the signs of a bloom before you take the plunge.

Don't go into water that looks foamy, scummy, thick like paint, pea-green, blue-green or brownish red. A good rule of thumb for you and your pet is: When in Doubt, Stay Out!

dogIf you believe you or your pet have been exposed to a cyanobacteria bloom, OHA staff are available to answer health related questions and to receive and document illness reports. We will also provide you with contact information for our partners who can give you the most up-to-date information about local recreation areas, water quality and sampling.

Be aware that dogs can suffer from heat stroke and water intoxication. Water intoxication occurs when dogs swallow too much water while fetching objects over an extended period of time without a break. These disorders can disrupt brain function causing symptoms like those associated with exposure to cyanotoxins.

Current Cyanobacteria Bloom Advisories

Oregon region map with advisory locationsThe most current information on advisories issued and lifted throughout the season.

View a map and table of current recreational use health advisories for cyanobacteria and cyanotoxins 

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Advisory Archive


A yearly presentation of recreational use health advisories issued in Oregon since 2007.

Browse the summaries and view the data for each year

Frequently Asked Questions

FAQ brochure cover

Answers to common questions about blue-green algae blooms.

Browse the list of FAQs or download the brochure in English or Spanish

Advisory and Sampling Guidance

Guidelines covers For lake managers and others who deal with cyanobacteria blooms.

View Advisory and Sampling Guidance

Education and Outreach

harmful algae bloom

Brochures, posters, fact sheets and journal articles that cover basic information, human health, animal health, fish consumption and environmental concerns.



A list of some agencies involved in responding to cyanobacteria blooms.

Activities include: lake management, public health protection, and shellfish safety closures