Island County is among 19 counties in Washington state officially in a state of emergency due to heavy rainfall.

And for good reason.

A manhole cover shot into the air and sewage poured out onto a city street in Oak Harbor Wednesday night. Untreated sewage is being pumped into the city’s harbor because the new treatment plant can’t keep up with a huge increase in the flow.

In Central Whidbey, about 25,000 gallons of “fine solids” from a sewage treatment plant spilled into Penn Cove due to flooding.

The National Weather Service reports that seven inches of rain have been measured at the weather station at Naval Air Station Whidbey Island so far this year. On average, four inches fall in January and February combined.

Oak Harbor declared an emergency water use restriction Thursday for commercial and residential water users in hopes of reducing the amount of water going to the sewage treatment plant.

City Engineer Jim Bridges explained that the flow peaked Wednesday afternoon and has stayed consistently high. The plant can treat 3 million gallons a day and treats 1.5 million gallons on a typical day. Between 5-6 million gallons a day are currently pouring into the plant.

Since the plant can’t keep up, about 900 gallons a minute of screened sewer water is being pumped into the harbor. He said he expects the discharging to continue until Sunday, when rain is supposed to stop.

“We don’t want the pumps running any longer than they have to,” he said.

The city advises people to avoid contact with the harbor water until the emergency has passed. The Washington State Department of Health closed shellfish harvesting in the area.

Bridges said rainwater is likely getting into the sewage lines through cross connections between sewer and stormwater pipes — which is a byproduct of days gone by when the two systems were connected — and through cracks in pipes.

The excessive rainfall has resulted in multiple sanitary sewer overflows. In one case, Bridges explained, a surge in a sewage trunk line caused a manhole to shoot in the air on Ely Street at about 10 p.m. Wednesday. City crews cordoned off the area and cleaned the liquids and solids that bubbled up onto the road, but about 50,000 gallons of the untreated stuff got into the stormwater system and was discharged into the harbor, the state Department of Ecology reported.

Under the city’s water emergency, citizens are asked to reduce all non-essential water use. The city suggests simple water-saving ideas like taking shorter showers, turning off water when brushing teeth, flushing toilets less and waiting to wash clothes until the rain stops.

Due to flooding, Fort Nugent Park and the east entrance to Windjammer Park at Bayshore Drive and City Beach Street are closed.

As Bridges pointed out, Oak Harbor’s treatment plant wasn’t alone in the region when it comes to rainwater trouble.

According to a spokesperson for the Department of Ecology, the Penn Cove Wastewater Treatment Plant was flooded by water from an adjacent wetland Wednesday night. The floodwater entered the aerobic digester, which holds fines solids that “come out of the process after bacteria break them down.”

About 25,000 gallons of the solids were swept into Penn Cove with the floodwater.

• Editor Jessie Stensland contributed to this article.