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PORTLAND, Ore. — People should avoid the Willamette River and Tryon Creek until at least Tuesday because of sewage overflows caused by this weekend's heavy rain.

The Bureau of Environmental Services said its combined sewer system started overflowing into the Willamette River at about 9:15 a.m. Sunday and continued into Sunday afternoon. The agency said Sunday it doesn't know how much leaked into the river.

The bureau advises people to avoid the river downstream from the Ross Island Bridge for 48 hours from the time the sewage overflows ended.

An unknown amount of sewage also overflowed from a manhole in the 9400 block of SW Lancaster Road in Portland on Sunday. The overflow was caused by the weekend's heavy rains as well as rags that clogged a sewer pipe.

The sewage flowed onto the street, into a private yard and may have reached Tryon Creek. Crews were able to clear the blockage and restore service at around 2 p.m. Sunday.

Portland Environmental Services said people should avoid Tryon Creek for 48 hours since the sewage overflow stopped.

The city says combined sewer overflows consist of about 80 percent storm water and 20 percent sewage. The city says sewer overflows were greatly reduced after the Big Pipe project was completed in 2011.

The Associated Press contributed to this report.