The Lagoon at Ross Island
Four of the past five summers have brought toxic cyanobacteria blooms to the Willamette in Portland. Researchers say the cause is a man-made lagoon, 120 feet deep from a century of gravel mining, and that restoring the river's flow through it is the fix. What would it take, and who pays?
Both claims are from "Restoring Ross Island is the solution to curbing toxic bacterial blooms in the Willamette, researchers say", Henry Brannan, Street Roots, 2026-07-08, read today. The article names Desirée Tullos of Oregon State University and the Human Access Project, a Portland nonprofit. Its account: in 1926 the US Army Corps of Engineers built an embankment that created the lagoon; from 1926 to 2001 Ross Island Sand and Gravel mined it to about 120 feet deep; the owner, Robert Pamplin Jr., was fined $14 million in 2026 over an unmet mitigation agreement; two restoration options would cut channels to restore flow and flush the lagoon, at $17 to 27 million, with about $500,000 needed for design.
Anselm's note, 2026-09-03: this river is near his home, and since the article ran there have been serious blooms this summer and nobody can swim in it. That is a record the piece can carry: Oregon Health Authority advisories by date, water temperature, flow.
Perennial question: a city that dug a hole in its river and what it costs to undo. Passes the filter. A small model: lagoon residence time against temperature and nutrient load, before and after each channel option.
claims it answers
- “The man-made lagoon's warm, stagnant, nutrient-rich water consistently causes the cyanobacteria blooms”
- “Four out of the past five years have seen significant blooms in the Willamette”
Real public claims, adjudicated on the piece itself, not here.