When in Doubt, Stay Out!

Cyanobacteria Harmful Algae Blooms (CyanoHABs)

Cyanobacteria blooms are a natural occurence in Oregon lakes and rivers. However, some blooms can produce cyanotoxins. The toxin-producing blooms are call cyanobacteria harmful algae blooms (cyanoHABS). Exposure to toxins from cyanoHABs can cause the following symptoms if swallowed:

Bad taste in mouth
Loss of appetitie
Malaise or lethargy
Headache or fever
Nausea, vomiting, or diarrhea
Bloody diarrhea
Blood in urine or dark urine
Acute hepatitis or jaundice
Tingling
Numbnes
Buring sensation
Drowsiness
Salivation
Sleep disturbances

Direct skin contact with cyanotoxins can cause skin rashes.

Children, people with weakened immune systems, and pets are most vulnerable to illness.

What do cyanoHABs look like?

CyanoHABs can take on many appearances and can occur in two places: floating in the water (planktonic) or on the bottom of lakes and rivers (benthic). It's important to recognize what these blooms look like to stay safe. Planktonic cyanoHABs can be bright green or blue-green paint, thick pea-green soup, white or brownish-red foam or scum. Benthic cyanoHABs can be attached to sand, rocks, or aquatic plants. They can be green, blue-green, or brownish-red. Benthic mat material can detach from the bottom and float to the surface of the water. This detached material can accumulate along the shore, and can even be dried on the beach.

See OHA's photo gallery for visual examples of cyanoHABS.

Oregon Health Authority (OHA) reviews available information on cyanobacteria harmful algae blooms (called CyanoHABs) in lakes and rivers. If conditons pose a health risk, OHA may issue a recreational advisory or precation.

OHA recommends that if you are not sure if a lake or river has a cyanoHAB, it is best to stay out of that waterbody and keep pets away. When in doubt, stay out!

Oregon Recreational CyanoHAB Program Presentation and Listening Session - December 11, 2025

Session Recording: https://www.youtube.com/watch?v=VgRYpaZEZY0

Questions and Answers-Oregon Recreational CyanoHAB Program Listening Session-December 11 2025.pdf

View Current Advisories FAQs

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

CyanoHABs and Cyanotoxins

CyanoHABs can occur in two places: floating in the water (planktonic) or on the bottom of lakes and rivers (benthic). It's important to recognize what these blooms look like to stay safe.

Benthic Cyanobacteria

The science surrounding benthic cyanobacteria, the mats they form and the toxins they produce is ongoing. Benthic cyanobacteria mats are found in clear water rivers and lakes and do not form the kind of scum people may be 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 can be harder for people to see than those that form scum or a bloom on the surface of the water, so knowing what mats look like and how they differ from surface water blooms can help reduce 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".

CyanoHAB 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!

If you believe you or your pet have been exposed to a CyanoHAB, 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 Recreational CyanoHAB Advisories

The most current information on recreational advisories issued and lifted throughout the season.

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

Recreational CyanoHAB 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

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

For lake managers and others who deal with cyanobacteria blooms.

View Advisory and Sampling Guidance

Education and Outreach

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