PORTLAND -- A brief, but heavy rain storm caused Portland's sewer system to send raw sewage into the Willamette River.

National Weather Service hydrologist Andy Bryant says as much as a third of an inch fell about 4 p.m. Monday.

The downpour flooded the city's combined sewage and rainwater system, discharging untreated water into the river for about 12 minutes.

Residents were warned to stay out of that area of the river until at least late Wednesday afternoon.

The discharge is the eighth since the city finished the $1.4 billion Big Pipe project in 2011. Before that massive underground tunnel project was completed, the city averaged 50 overflows each year.

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