Beware of Cyanotoxins in Lakes and Rivers

As summer gets into full swing, the Oregon Health Authority (OHA) reminds people heading outdoors to enjoy Oregon’s lakes, rivers and reservoirs to be on the lookout for potentially toxic cyanotoxins. Cyanotoxins are produced by cyanobacteria, a beneficial bacteria found in freshwater worldwide. The bacteria is beneficial, but under the right conditions–warm weather, sunlight, water temperature, nutrients and water chemistry–it can produce cyanotoxins that make people and animals sick.

Exposure to cyanotoxins occurs when water is swallowed while swimming or breathing in water droplets during high-speed activities such as water skiing or wakeboarding. Children and pets are particularly sensitive because of their size and activity levels. Dogs can get extremely ill and even die within minutes to hours of exposure to cyanotoxins by drinking the water, licking their fur or eating the toxins from floating mats or dried crust along the shore.

Symptoms of exposure to cyanotoxins include diarrhea, cramps, vomiting, numbness, dizziness and fainting. If these symptoms occur for more than 72 hours, people should seek medical attention to avoid dehydration. Dogs will exhibit symptoms quickly, after the first hour of exposure, and should be taken to a veterinarian as soon as possible when symptoms (including breathing problems, difficulty walking/standing or loss of appetite) are present. Although cyanotoxins are not absorbed through the skin, people with sensitive skin can develop a red, raised rash when wading, playing or swimming in or around a bloom.

Only a fraction of freshwater bodies in Oregon are monitored for cyanotoxins. For this reason, it’s important for individuals to carefully observe any body of water they choose to recreate in before jumping in.

OHA recommends that everyone stay out of water that looks foamy, scummy, thick like pea green or blue-green paint or where brownish-red mats are present. Additionally, since blooms can also wash up on the shore, avoid areas with algal mats that are either attached, floating or stranded on the shore. Find pictures of algae blooms at and on OHA’s YouTube video, “When in doubt, stay out” at

Even then, looks can be deceiving. Certain blooms can grow on or near the bottom of lakes and rivers. While some of them make and release toxins into the water, they don’t change how the surface of the water looks, making them hard to see.

Recreational areas where blooms are identified can still be enjoyed for activities such as camping, hiking, biking, picnicking and bird watching. With the appropriate precautions, water activities like canoeing, boating and fishing can also be enjoyed as long as speeds do not create excessive water spray and fish are cleaned appropriately. 

To learn if an advisory has been issued (or lifted) for a specific body of water, visit the Harmful Algae Bloom website at or call 877.290.6767.

Beware of Cyanotoxins in Lakes and Rivers

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top