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Recreational use advisory lifted for Oswego Lake

Oregon Health Authority sent this update at 10/15/2025 01:14 PM PDT

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Oct. 15, 2025

Media contact: Erica Heartquist, PHD.Communications@oha.oregon.gov

Recreational use advisory lifted for Oswego Lake

Continue to keep pets away as levels detected remain above educational guideline values for animals

PORTLAND, Ore.—Oregon Health Authority (OHA) has lifted the recreational use health advisory issued for Oswego Lake in Clackamas County.

OHA issued the advisory Sept. 30.

Water monitoring has confirmed that the level of cyanotoxins in Oswego Lake are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.

OHA advises recreational visitors to continually be alert to signs of cyanobacteria blooms. 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.

When recreating, people, and 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 brownish-red mats are visible or bright green clumps are suspended in the water. If you see these signs, 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.

Cyanotoxins can still exist in clear water. When a bloom dies, toxins released may reach into clear water around the bloom. Blooms can be pushed into other areas, leaving toxins behind. There also are species of cyanobacteria that anchor themselves at the bottom of a water body, live in the sediment or can grow on aquatic plants and release toxins into clear 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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