DC Water officials estimate that 200 million gallons of rain mixed with raw sewage overwhelmed pumping stations and poured into waterways around the city during the downpour from Hurricane Irene.

The sewer overflow contributed to a flood of wastewater into rivers and streams over the weekend. The Maryland Department of the Environment reported that the storm caused the release of millions of gallons of waste into streams and rivers that flow into the Chesapeake Bay.

Wastewater combined with rain overflowed Baltimore County pumping stations a dozen times, the agency reported,and wastewater plants at several towns on the Maryland Eastern Shore also overflowed.

“Overflows are . . . quite common throughout Maryland, throughout the region, and throughout even the U.S,” Jay G. Sakai, director of the Water Management Administration of the state agency, told the Bay Daily, which is published by the Chesapeake Bay Foundation. “This is a problem that we all have to work together to help fix.”

The pounding rain caused the Fort Washington pumping station to spill about 61,200 gallons into the Piscataway Creek, said Lyn Riggins, a spokeswoman for the Washington Suburban Sanitary Commission.

That overflow began at 1:21 a.m. and ended at 12:52 p.m. Sunday, Riggins said. WSSC notified the Maryland Department of the Environment and the Prince George’s County Health Department of the incident.

Like Maryland, sewer overflows are common in the District, where antiquated Civil War-era pipes are often overwhelmed, said a spokeswoman for DC Water.

When rain runoff combines with water that’s flushed and drained in businesses and homes, the system backs up. Rather than allow water to bubble up in sinks and toilets, wastewater systems release it into the nearest body of water.

As a result, the level of fecal coliform that contains human waste far exceeds acceptable levels following rains. It is one reason the District’s health department maintains a ban on swimming in the city’s rivers and creeks.

DC Water’s Clean Rivers team said nearly four inches of rain fell during Hurricane Irene.

“Potentially harmful substances may also be present in these discharges,” according to DC Water’s Web site. “For larger rainfalls, greater than 1 inch . . . effects . . . on water quality can last up to three days.”