Officials test for possible toxic algae in Oregon river

PORTLAND, Ore. (Reuters) - Tests are underway to determine if a green film shimmering on the surface of Portland's Willamette River may mark the return of toxic blue-green algae that could be dangerous to both people and animals, officials in Oregon said on Thursday.

The concerns come as dozens of people from across the country have signed up to participate in the 10.7 mile Portland Bridge Swim at the weekend, said Travis Williams, executive director of Willamette Riverkeeper, a nonprofit that reported algae concerns to public health officials.

"From a preliminary look conducted in Portland, it looked like microcystis, the toxic blue-green algae, but that's totally unofficial," Williams said.

Oregon Health Authority officials said on Thursday they were unable to provide information about when official test results might be available.

Until last year, when riverside homeless camps were cautioned to avoid the water and a rowing regatta was canceled, state public health authorities had not previously spotted toxic algae in Portland's Willamette River, which bisects the city and is a hub of recreation and industry.

Toxic algae blooms have been a growing problem in the U.S. Pacific Northwest during the past several years, a trend scientists attribute to warming waters.

But typically, microcystis is found in still water, like lakes and ponds, not fast-flowing rivers. And last year's algae blooms were not detected until September, after snow from nearby mountains had fully melted, river levels had dropped and water had begun to warm.

"This is indicative of unusual conditions this year, especially this early in the year," Williams said. "We have low water flows, which makes the lower Willamette very lake-like. The water temperatures are high, and nutrient levels could feed algae."

Swallowing or inhaling water contaminated by the toxic algae can cause numbness, digestive distress or fainting, and skin contact can cause a rash. Filtering the water will not make it safe, and fish or shellfish from the river could be dangerous to eat, according to the Oregon Health Authority.

Dogs are particularly vulnerable, and can die within an hour of contact, according to the agency.

(Editing by Cynthia Johnston and Sandra Maler)