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April 17, 2025
Media contact: Timothy Heider, 971-599-0459, PHD.Communications@oha.oregon.gov
OHA to issue algae warnings when dog deaths reported
New notifications will indicate possible cyanobacteria blooms
PORTLAND, Ore.— As summer approaches, Oregon Health Authority (OHA) reminds people heading outdoors to enjoy the state’s lakes, rivers and reservoirs to be on the look-out for potentially toxic cyanobacteria blooms.
To help, OHA is adding a tool reporting the possible presence of cyanobacteria in freshwater lakes and rivers statewide. Starting immediately, OHA will issue pre-emptive public warnings following reports of dog illnesses or deaths possibly resulting from cyanotoxin exposure.
“Each year, we receive reports about dog illnesses or deaths linked to a water body that may be affected by cyanobacteria, but the deaths are often unexplained, or the cause of the death isn’t immediately known,” said Linda Novitski, Ph.D., a recreational waters specialist in OHA’s Environmental Public Health Section.
“These pre-emptive warnings will help us immediately takes steps to inform the public about the possible presence of cyanobacteria in a water body,” she said.
Toxin testing is only possible for certain types of cyanobacteria. When testing is done, results are typically available within two weeks.
Cyanobacteria are beneficial bacteria found in all 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.
Many blooms are harmless, but some can produce cyanotoxins that make people and animals sick. Exposure to cyanotoxins occurs when water or algae mat material is swallowed while swimming, or when people inhale water droplets during high-speed activities such as water-skiing or wakeboarding. Symptoms of exposure to cyanotoxins include:
- Diarrhea
- Cramps
- Vomiting
- Numbness
- Dizziness and fainting
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.
Some species of cyanobacteria live in the water or float on the top of the water surface. Other cyanobacteria, called cyanoHAB mats, anchor themselves to the bottom of a water body, live in the sediment, or grow on rocks or aquatic plants can release toxins into clear water. These bloom mats contain toxins that, if ingested, can be fatal to dogs and can make people sick.
Dogs can get extremely ill, and even die, within minutes to hours of exposure to cyanotoxins by drinking the water. Problem signs include licking their fur or eating 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.
“Enjoying lakes and rivers is such an important part of the Oregon experience,” said Novitski. “To have fun and stay safe this season, protect small children and dogs by avoiding anything you think might be a cyanobacteria harmful algae bloom in the water or in a mat attached to the bottom of the lake or river.”
Cyanotoxins can still exist in clear water. When a bloom dies, toxins it released may reach into clear water around the bloom. Blooms can be pushed into other areas, leaving toxins behind.
OHA advises recreational visitors to always be alert to signs of cyanobacteria blooms in the water and in mats attached to the ground or rocks. This is because blooms can develop and disappear on any water body at any time when bloom conditions are favorable.
Only a fraction of water bodies in Oregon are monitored for blooms and toxins, so it’s important for people to become familiar with signs of a bloom, exposures and symptoms by visiting OHA’s Cyanobacteria (Harmful Algae) Blooms website at http://www.healthoregon.org/hab.
An example of a cyanoHAB mat.
Mats like these can detach from rocks and float to the surface.
When recreating, people—especially small children—and pets should avoid areas where 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.
If those signs are noticeable, people are encouraged to avoid activities that cause you to swallow water or inhale droplets, such as swimming or high-speed water activities, and keep pets out of the area.
Community members looking for visual examples can find pictures of algae blooms in the Algae Bloom 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.”
 OHA YouTube video, “When in Doubt, Stay Out: Cyanobacteria Blooms.”
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, local communities 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.
For health information or to report an illness, contact OHA at 971-673-0440, or visit OHA’s Cyanobacteria (Harmful Algae) Blooms website.
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