A state agency has lifted a public health advisory, allowing people to again recreate on parts of the Willamette River in Portland.

The Oregon Health Authority based the decision on water samples from Ross Island Lagoon and Holgate Channel. The agency said cyanobacteria, or blue-green algae, levels are below recreational guidelines for adults but warned that levels are still toxic for dogs and children.

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A mostly-blue river adjacent to a strip of land and green water on the other side.

An aerial view on Aug. 19, 2021 of algal blooms in the Ross Island Lagoon, to the right of the Willamette River's mainstem.

Brandon Swanson / OPB

If ingested, the cyanobacteria can make people sick or cause skin, eye and ear irritation if exposed. The Oregon Health Authority warns the public to be aware of signs of the cyanobacteria which can look foamy, scummy, or like thick blue-green paint on the river. as they can develop or bloom at any time when conditions are favorable.

Cyanobacteria bloom on an annual basis and at any time when conditions are favorable— like warm, slow moving waters that are rich in nutrients like phosphorus and nitrogen. The density and extent of the bloom depends on year to year.

The recreational advisory was issued by the agency on Aug. 31.

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