Hundreds of cities across the country have old sewer systems that were designed to overflow into the nearest waterways, many of them dumping billions of gallons of untreated waste into rivers and lakes every year. But fixing the problem costs a lot of money, and many cities are now struggling to pay for sewage projects mandated by the federal government. Jacob Fenston reports from member station WAMU here in Washington.

JACOB FENSTON, BYLINE: Ever since Washington, D.C., was founded more than 200 years ago, sewage from the city has polluted the Potomac River and the smaller Anacostia River. To get a view of the problem up close, I hopped in a boat with Jim Foster.

JIM FOSTER: So we're underneath the 11th Street Bridge here. We're going to swing around and get...

FENSTON: Foster is president of the Anacostia Watershed Society. He maneuvers the boat around bridge pilings up to a large opening on the shore. This is a combined sewer outfall. There are 47 of them lining the banks of the rivers here. When it rains, sewage spills out 70 to 80 times a year.