Toxic blooms from the Ross Island lagoon, Portland

Ross Island was a chain of natural islands in the Willamette River until 1926, when the US Army Corps of Engineers built an embankment on the south-east side and turned the middle into a lagoon.¹ Gravel was mined from it until 2001, to a depth of about 120 feet.¹ The lagoon's warm, stagnant, nutrient-rich water now breeds cyanobacteria (blue-green algae) blooms that close the river to people, and four of the past five years have had significant blooms.¹ Exposure can cause headaches, fever, vomiting and worse.¹ A research partnership between Oregon State University, led by Desirée Tullos, and the Portland nonprofit Human Access Project presented two designs in June 2026: remove the lagoon's south-west wall, or cut that channel plus a second on the north-west side.¹ Both let the river flush the lagoon faster than the water warms and bacteria grow, at roughly $17 million or $27 million.¹ About half a million dollars more is needed to finish design and permitting, and no one has yet committed to pay.¹

Who needs an answer

• The State of Oregon, which the project's backers want to name a lead, set a timeline and find the money.¹
• The Oregon Department of State Lands, which, Willamette Week reported, fined the owner of the mining company $14 million in 2026 for failing to make progress on a 2023 agreement to mitigate the mining damage.¹
• Portland Parks and Recreation, Metro and Multnomah County, among those the researchers thanked as partners, funders and supporters, with a stake in a river whose riverfront parks draw 1.2 million visits a year and where recreation brings in about $120 million in spending.¹
• Prospective buyers who have proposed filling the pit with contaminated Superfund sediment from the river downstream.¹

The domains it chains

River flow and how it moves through the lagoon; water temperature and nutrients; cyanobacteria growth and toxins; public health; swimming, boating and events on the river; mining law and the owner's obligations; and the city's earlier spending on cleaner water, more than a billion dollars on the Big Pipe project.¹

What a twin should let people try

• Designs: how fast each channel option replaces the lagoon's water in a hot, low-flow summer, and whether that beats bloom growth.
• Together: whether filling the deep pit with sediment changes what the channels achieve; the researchers' models found it would not stop the channels flushing the surface or remove the need for them.¹
• Warming: how the blooms respond as summers get hotter, with and without the channels.

Where to start

The Oregon State team's 73-page report sets out the designs and models.¹ For tracking blooms from space, CyFi estimates cyanobacteria density in small lakes and reservoirs from Sentinel-2 imagery.