Toxic Algae Bloom Makes the Willamette River Hazardous for Swimming, Just as Heat Wave Arrives

Dogs and children run the highest risk of getting severely ill from green algae.

NOT THIS WEEK: Don't go for a float at Riverplace Marina in the Willamette River. (Danny Fulgencio/Danny Fulgencio)

When temperatures crest 100 degrees in Portland, as they probably will this coming week, many residents like to beat the heat with a dip in the Willamette River, especially in places like Oaks Bottom and Riverplace Marina.


State and county health officials warn that a toxic algae bloom in Ross Island Lagoon has spread into the Willamette, making swimming, jet skiing and power boating dangerous because all those activities run the risk of swallowing river water.

“Terrible timing with the weather,” says Multnomah County spokeswoman Julie Sullivan-Springhetti. The Oregon Health Authority issued the algae warning Friday, and she’s been building maps of no-swim zones and trying to get the word out ever since.

No-Swim Zone

Dogs and children run the highest risk of getting severely ill from green algae. “Dogs can get extremely ill and even die within minutes to hours from exposure to the toxins by drinking the water, licking their fur, or eating the toxins from floating mats or dried crust along the shore,” the county says in a statement.

OHA still hasn’t identified what kind of algae is spreading out of Ross Island Lagoon, which regularly plays host to such flare-ups when the water warms.

In April, the Northwest Environmental Defense Center sued OHA over a permit the agency issued to Ross Island Sand & Gravel in 2022, allowing it continue a 40-year job of refilling the pit where it once mined gravel. The lawsuit says OHA failed to require the gravel company, part of R.B. Pamplin Corp., to maintain water quality while finishing the work.

Other algae blooms are occurring down the river at Willamette Cove, and on Sauvie Island on Aarons Lake, Pete’s Slough and Sturgeon Lake.

The National Weather Service predicts temperatures at or just above 100 degrees on Monday and Tuesday, before dipping back into the 90s midweek.

County officials say they’ll announce the opening of severe weather shelters closer to the heat wave’s Sunday arrival. If you’re looking for some other place to cool off, Portland Parks & Recreation has installed misting stations (PVC pipe spraying a cool drizzle) at more than a dozen parks, listed below. They run 24 hours a day.

• Argay Park (3898 NE 141st Ave.)

• Glenhaven Park (8000 NE Siskiyou St.)

• Floyd Light Park/Rose Petal Fountain (10620 SE Stark St.)

• Harney Park (8498 SE 67th Ave.)

• Holladay Park (1198 NE Multnomah St.)

• Knott Park (2505 NE 117th Ave.)

• Lents Park (4603 SE 92nd Ave.)

• Lynchwood Park (17301 SE Haig St.)

• McKenna Park (7129 N Wall St.)

• Mt Scott Community Center (5527 SE 72nd Ave.)

• Normandale Park (1260 NE 57th Ave.)

• Powell Park (curb service south of Southeast Powell Boulevard on 22nd Avenue)

• Wilshire Park (3350 NE Skidmore St.)

• Woodstock Park (4701 SE 47th Ave.)

Willamette Week’s reporting has concrete impacts that change laws, force action from civic leaders, and drive compromised politicians from public office. Support WW's journalism today.