Willamette River Algae 2025. Blooms of harmful algae are common in the willamette river during the summer months. The algae bloom in the willamette river as it passes through downtown portland continues to make the water hazardous for recreational use, and state health experts say we need cooler.
Portlanders looking for a break from the heat should avoid the willamette river between cathedral park and ross island because of a toxic algae bloom, the oregon health. Algae blooms near the lagoon turn the water green.