When In Doubt, Stay Out: Increasing Temperatures Create Potential For Toxins In Water -05/22/25
May 22, 2025
Media contact: Erica Heartquist, PHD.Communications@oha.oregon.gov
When in doubt, stay out: Increasing temperatures create potential for toxins in water
PORTLAND, Ore.—As summer approaches, and the water quality monitoring season begins, Oregon Health Authority (OHA) reminds people heading to the state’s lakes, rivers and reservoirs to be on the look-out for potentially toxic cyanobacteria harmful algae blooms.
Cyanobacteria are beneficial bacteria found in most fresh water worldwide. The bacteria can multiply into blooms in any water body under the right conditions—warm weather, sunlight, water temperature, nutrients and water chemistry.
Some species of cyanobacteria live in the water or float on the top of the water surface. Other cyanobacteria mats anchor themselves to the bottom of a water body, live in the sediment, or grow on rocks or aquatic plants, and can release toxins into clear water.
Some blooms can produce cyanotoxins that make people and animals sick. They can make the water look green or other colors and form scum-like masses or mats in water or on shore where they can be wet or dry.
“As the warmer weather draws us to Oregon’s lakes and river, people—especially small children—and pets should avoid areas where there are signs of a cyanobacteria bloom, the water is foamy, scummy, thick like paint, pea-green or blue-green, or if thick green or brownish-red mats are visible, or bright green clumps are suspended in the water or along the shore,” said Linda Novitski, Ph.D., a recreational waters specialist in OHA’s Environmental Public Health Section.
Although cyanotoxins are not known to be absorbed through the skin, people with sensitive skin can develop a red, raised rash when wading, playing or swimming in or around a bloom.
Children and pets are particularly sensitive to illness because of their size and activity levels. Similarly, livestock and wildlife can become ill and die after drinking from water bodies, troughs or other sources of drinking water affected by blooms and potential toxins.
Dogs can get extremely ill, and even die, within minutes to hours of exposure to cyanotoxins by drinking the water. OHA issued this news release about the dangers of cyanotoxins to dogs. The agency issues pre-emptive public warnings following reports of dog illnesses resulting from cyanotoxin exposure. Exposures occur when dogs lick their fur or eat the toxins from floating mats or dried crust along the shore.
If, after swimming in a lake or stream, a dog exhibits symptoms such as diarrhea, vomiting, breathing problems, difficulty walking or standing, or loss of appetite, owners should get their pet to a veterinarian as soon as possible.
Open recreational areas where blooms are identified can still be enjoyed for activities such as camping, hiking, biking, picnicking and bird watching.
By being aware of signs of a bloom and taking appropriate precautions to reduce or eliminate exposure, visitors can enjoy water activities such as canoeing, boating and fishing, as long as boat speeds do not create excessive water spray, and fish are cleaned appropriately.
Only a fraction of water bodies in Oregon are monitored for blooms and toxins, so it’s important for people to become familiar with the signs of a bloom by visiting OHA’s CyanoHAB website at http://www.healthoregon.org/hab.
Community members looking for visual examples can find pictures of blooms in the CyanoHAB Photo Gallery or watch an explainer video on blooms at OHA’s official YouTube channel.
Those who are unsure should follow OHA’s guidance of “When in doubt, stay out.”
For health information or to report an illness, contact OHA at 971-673-0440, or visit OHA’s CyanoHAB website.
###
