PORTLAND, Ore. — Portland issued a combined sewer overflow (CSO) advisory for the Willamette River Tuesday as the city's Big Pipe system hit 100% capacity.

Although the city's Big Pipes have led to a dramatic reduction in the frequency of these overflows, the Pacific Northwest was hammered by rain Monday night into Tuesday morning.

Portland's online Big Pipe tracker showed that the system hit max capacity, causing the overflow, around 3:15 a.m. on Dec. 9. The pipes were full all day until shortly before 9 p.m. As Wednesday morning, the pipes had drained down to 17% capacity.

People should avoid contact with the stretch of the Willamette River downstream of the Ross Island Bridge — U.S. 26 — until Portland lifts the advisory.

A CSO consists of roughly 80% stormwater and 20% se

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