CSO Advisory: Combined sewer overflow to the Willamette River from a single outfall near Willamette Park

The public is advised to avoid contact with the Willamette River downstream of Willamette Park for 48 hours due to the potential presence of increased bacteria in the water. The river’s water quality is safe for recreation during all other times.

This outfall is not connected to the Big Pipe system. The Big Pipe was less than 20 percent full at the time and continues to prevent overflows from other locations.

About combined sewer overflows

A combined sewer overflow is typically about 80 percent stormwater and 20 percent sewage. These events are rare and can occur during periods of heavy precipitation.

About the Big Pipe Project

Since completing the Big Pipe project in 2011, the 20-year $1.4 billion program to reduce overflows, the number of CSOs has dropped by 94 percent to the Willamette River and 99 percent to the Columbia Slough. Before the project, incidents occurred to the Willamette River an average of 50 times a year, with some lasting days. 

Today, overflows occur an average of four times per winter season and once every three summers. Single-outfall events, like today’s, can happen when localized storms overwhelm a small part of the system.

About Environmental Services

Environmental Services – the City of Portland’s sewer and stormwater utility – protects public health and the environment by collecting and recovering resources from the city’s wastewater, managing stormwater, and restoring and protecting Portland’s rivers, streams, and watersheds.