Whenever it rains in Washington, D.C., raw sewage spills into the Potomac River because of the city’s outdated sewer system. These Combined Sewer Overflows release pollutants like fecal coliform bacteria and e. coli into the waterway, potentially sickening animals, fish, and humans, and depleting the oxygen levels causing harmful algal blooms. After the Storm investigates the all-too-common problem of wastewater overflows, and reveals a remarkable network of underground tunnels being constructed below the nation’s capital to try to stem the toxic tide that threatens the Potomac River and the Chesapeake Bay.