American Rivers, an environmental advocacy group, has named the Delaware as its river of the year for 2020, hailing it as a “national success story” for its dramatic revitalization from the decades it spent polluted by industrial and sewage waste.

“The Delaware shows how a healthy river can be an engine for thriving communities and strong local economies,” William Robert Irvin, president and CEO of American Rivers, said in a news release.

At 330 miles long, the Delaware is the largest undammed river in the United States east of the Mississippi. It runs from Hancock, N.Y., to the Delaware Bay, from which it eventually empties into the Atlantic Ocean. Along the way, it is fed by 2,000 tributaries, the largest being the Schuylkill and the Lehigh River in Pennsylvania.

From Trenton to the Delaware Bay, the river is tidal and is known as the Delaware Estuary, where the river’s freshwater mixes with saltwater from the ocean.

Today, the river is far cleaner than when it was heavily polluted from at least the late 1800s through the mid-1900s, when it was choked with dead zones of aquatic life. Now, fish such as American shad and striped bass have made a comeback. Bald eagles, once nearly extinct, now depend on its bounty.

The river also provides drinking water for more than 13 million people, including those in New York City and Philadelphia.

The river’s improvement is credited to a number of initiatives, including the federal Clean Water Act, the policies of four states (Pennsylvania, New Jersey, New York, and Delaware), regulation by the Delaware River Basin Commission, and, more recently, the Delaware River Watershed Initiative, a coordinated effort of dozens of environmental groups and research organizations. The Delaware has the most extensive National Wild and Scenic River protection of any watershed in the country.

“Communities along the Delaware River are setting a national example for river stewardship,” Irvin said. “We must use these lessons to ensure healthy rivers, equitable access, and clean water in cities nationwide.”

Irvin added that continued “commitment from leaders and local communities is critical to address growing challenges such as aging water infrastructure, urban development, and climate change.”

American Rivers also released a list of America’s Most Endangered Rivers of 2020.