Heavy rains turned streets in the Portland area into creeks, interrupted bus and light rail service and forced the evacuation of at least one neighborhood.

Monday's flooding caused the closure of numerous roads, and heavy rains triggered landslides.

The rain also caused Portland's sewer system to overflow into the Willamette River. Officials said people should avoid contact with the river for at least 48 hours because of bacteria in the water.

A big sinkhole developed in a street in Gresham, a Portland suburb. Crews were pumping water from an elementary school in Gresham, as well as cleaning up hallways and classrooms.

The parking lot at Multnomah Falls, a popular tourist stop in the Columbia River Gorge east of Portland, was closed after a creek overflowed its banks.

In Lake Oswego, just south of Portland, several cars were stranded in high water.

Residents were evacuated from a neighborhood in Clackamas County, and the American Red Cross was opening a shelter there.

Several school districts in northwest Oregon sent students home early and canceled afternoon and evening activities. The Oregon Zoo in Portland also closed.

The National Weather Service issued a flood watch for much of northwest Oregon and southwest Washington. It's in effect through Thursday afternoon, but rain likely won't stop until the week's end, forecasters said.

Excessive rainfall could lead to a rise in area rivers, weather officials said.

Officials say residents should avoid traveling and should watch for flash floods, mudslides, falling trees and power outages. They are also advised to keep children and pets away from floodwaters and avoid walking and driving through high water. Residents whose property is at risk for flooding should use sandbags.

The rains are caused by several low-pressure systems moving through the region, one after the other, forecasters said.