Portland completed the Big Pipe Project in 2011 to eliminate almost all sewage releases to Portland's Willamette River and Columbia Slough.

Overview: 94% reduction in combined sewer overflows (CSOs) to the Willamette River 
99% reduction to the Columbia Slough
Before CSO control: An average of 50 Willamette River CSO events each year.
Today: An average of four CSO events each winter and one every third summer.

100%: Eliminating all CSOs, instead of 94%, would have doubled the $1.4 billion project cost

Lesley Stahl narrates Portland's CSO Program, a video overview of Portland's 20-year program to control combined sewer overflows. The overall program became known as the Big Pipe Project. 

Cornerstone projects - downspout disconnections, sumps, stream diversions and sewer separations - removed millions of gallons of stormwater from combined sewers to allow construction of smaller CSO control facilities.

Big Pipes - one on the Columbia Slough, two on the Willamette River - intercept combined sewage and stormwater and direct it to the treatment plant.