D.C. has been making progress cleaning up the Anacostia and Potomac rivers, to the point where those long-polluted waterways could soon be safe to swim in. But recently, management at D.C.’s water and sewer authority has been considering scrapping a major part of the cleanup project, potentially continuing to dump more than 600 million gallons of sewage into the Potomac each year, for years to come.

The court-mandated project is known as Clean Rivers, and it’s one of the biggest — and priciest — infrastructure projects in the city since Metro was built. It consists of 18 miles of tunnels; they’re wider than Metro tunnels, and deeper underground. The whole project has a price tag of $2.7 billion. The vast majority of that is being paid for by residents with a Clean Rivers fee — currently $21 a month (about a fifth of the average residential water bill).