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July 2, 2026
Media contact: Jonathan Modie, PHD.Communications@oha.oregon.gov
Recreational use advisory issued for Thief Valley Reservoir July 2
PORTLAND, Ore.—Oregon Health Authority (OHA) issued a recreational use health advisory today for Thief Valley Reservoir due to laboratory results from recently-collected water samples that showed cyanotoxins above recreational use value (RUV).
A recreational use health precaution has been in place since June 12 due to the presence of a visible bloom. The lake is in Baker and Union Counties.
People should avoid swimming and other water activities with a high risk of swallowing water or inhaling water droplets in areas of the lake where blooms are present. Ingestion or inhalation of water is the exposure route of concern. Toxins are not absorbed through the skin. However, those with skin sensitivities may get a puffy red rash.
OHA’s RUVs are designed to protect the most vulnerable, including children, who have a higher activity level and are more likely to swallow water while recreating.
OHA encourages people to visit Thief Valley Reservoir and enjoy activities such as fishing, camping, hiking, biking, picnicking, bird watching, canoeing, and kayaking. Boating is safe as long as speeds do not create excessive water spray. Sprays could lead to the risk of inhaling cyanotoxins.
Drinking water
Drinking water directly from areas of the lake affected by a bloom is especially dangerous. Toxins cannot be removed by boiling, filtering or treating water with camping-style filters. Contact campground management or the local health department with questions about water available at nearby campgrounds or day use areas.
Not all private treatment systems are effective at removing cyanotoxins. People who do not use a well or public water system and draw in-home water directly from an affected area are advised to use an alternative water source for drinking and cooking.
Symptoms for people, pets
Children and pets are at increased risk for exposure because of their size, level of activity, and likelihood of swallowing water.
For people, exposure to cyanotoxins can be serious and cause a range of symptoms. Symptoms may be similar to food poisoning such as stomach cramps, diarrhea, nausea and vomiting. Symptoms may also be more serious, such as numbness, tingling, dizziness and shortness of breath. These symptoms may require medical attention.
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 crusts along the shore. This is regardless of whether a recreational use health advisory in place. Symptoms in dogs can include difficulty walking, seizures, lethargy, and loss of appetite, and more. If a dog exhibits symptoms, veterinary treatment should be sought as quickly as possible. OHA recommends keeping dogs on leashes, away from affected water and mat material, to help reduce the chance of exposure.
Fishing
Fish caught from areas where cyanobacteria blooms are present may pose unknown health risks, so OHA recommends not eating fish from those areas. Those who decide to eat the fish should remove fat, skin and organs, where toxins are more likely to build up, before cooking or freezing. Fillets should also be rinsed with clean water.
For health information or to report an illness, contact OHA at 971-673-0482, or visit OHA’s Cyanobacteria (Harmful Algae) Blooms website.
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