Willamette River goes sewer overflow-free thanks to Big Pipe system in Portland, Ore.

(UI) — Portland recently marked a major environmental milestone: one full year without a combined sewer overflow (CSO) into the Willamette River, a testament to the long-term success of the city’s $1.4 billion Big Pipe Project.

The achievement highlights how major infrastructure investments can deliver lasting benefits. Before the Big Pipe Project was completed in 2011, Portland averaged 50 CSO events per year into the Willamette—some lasting for days. Today, overflows to the river have been reduced by 94%, and by 99% to the Columbia Slough.

The milestone was commemorated by a celebratory swim hosted by the Human Access Project, a local group that advocates for safe and clean river recreation.

“Going a year without a combined sewer overflow would not be possible without the Big Pipe Project,” said Environmental Services Director Dawn Uchiyama. “This milestone is a powerful reminder that our investments in infrastructure have lasting and meaningful impacts on our community. Thanks to the Big Pipes, Portlanders' relationship and connection to the Willamette River has been transformed.”

The Big Pipe Project took 20 years to complete and has since significantly improved water quality in the Willamette. With the reduction in overflows came a drop in E. coli bacteria, making the river safe for recreation most days of the year. Kayaking, swimming, and paddleboarding have become increasingly popular as public confidence in the river's health grows.

“While the Big Pipe System is impressive in scale, the work that went into designing, constructing, and now operating and maintaining the Big Pipes is equally impressive,” said Priya Dhanapal, Deputy City Administrator for Public Works. “The work that we do and the strategic investments we make help shape the future of our city and are essential to protecting our natural resources for generations to come.”

The Big Pipe Project is part of Portland’s broader sewer and stormwater network, managed by Environmental Services. The Bureau oversees more than 2,000 miles of sewer pipes, nearly 3,000 green street planters, 100 pump stations, and two wastewater treatment plants. It also restores hundreds of acres of natural habitat citywide.

Environmental Services continues to invest in upgrades, including the $515 million Secondary Treatment Expansion Program (STEP) at the Columbia Boulevard Wastewater Treatment Plant—the largest since the 1970s. STEP aims to increase capacity and efficiency while protecting the environment for future generations.

While this one-year CSO-free milestone is significant, it is not Portland’s longest. The city previously went 499 days without a CSO between August 2019 and December 2020. Ongoing investments in infrastructure and resiliency aim to make these clean water milestones even more common.

Related News

From Archive

• Most Read
• Most Commented