Like any freshwater river, the Anacostia River is fed by a network of springs, creeks and streams that eventually merge to form the main stem of the river.

This stream network is known as the watershed. The Anacostia’s watershed is about 176 square miles. The entire watershed is contained in a small part of Montgomery County, a small part of Prince George’s County, and a small part of the District.

Except for the part of the District that was developed before about 1900, the entire Anacostia watershed is served by what is called a Municipal Separate Storm Sewer System (MS4). In this system, all of the water that falls on hard surfaces is conveyed directly to the nearest stream, and eventually to the main stem of the Anacostia. On the way, it picks up many kinds of contaminants, and creates erosion in many small streams and creeks. If it weren’t for this street contamination and erosion, the Anacostia would look a lot like pure, clean rainwater!

The oldest parts of the District are served by a “combined sewer system” that blends stormwater runoff and wastewater from houses and buildings in a single set of pipes. The combined sewer and wastewater is sent to the Blue Plains Advanced Wastewater Treatment Plant – except sometimes there is too much water for the system to handle. Unfortunately, the system is sized for pre-1900, and there is today far more concrete and asphalt, and far more wastewater than there was then. When the capacity of the pipe system is overwhelmed, it overflows and sewage is released directly into the waterbodies. DC Water, the District's water utility is currently building large storage tunnels to dramatically expand the system’s storage capacity and nearly eliminate overflows.

It is critically important for all three jurisdictions – Montgomery, Prince George’s and DC – to implement ways to retain, reuse, and filter stormwater runoff close to where it falls. Each jurisdiction is doing a lot, each in its own way. It’s not cheap, and it’s not easy. But it is critical if we are ever going to have a clean and healthy Anacostia.