A new report by the Potomac Conservancy, a local environmental advocacy group, finds that the river after which it’s named has improved dramatically during the past several years—receiving a grade of B- in 2016.

That’s up from a total grade of C in 2013 and D in 2011, according to the organization, which releases such a report biennially (this is its ninth). A large part of the improvement involves a decrease in pollutants like nitrogen, phosphorous, and sediment; in excessive amounts, these can make rivers unsafe for humans and wildlife. The Conservancy also attributes the Potomac’s betterment to more-robust game fish populations.

“Our hometown river—the source of drinking water for nearly five million residents—is worth saving,” said Potomac Conservancy President Hedrick Belin in a release. “We’ve made tremendous progress towards achieving our goal of a fishable, swimmable Potomac by 2025. But the Potomac is not in the clear yet.”

In terms of pollution, the report finds that 95 percent of the 104 wastewater-treatment plants that flow into the Potomac meet Environmental Protection Agency standards for emissions. Pollutants have dropped in the short- and long-term, since 2004 and 1985. But “polluted urban runoff—the only growing source of pollution to the Potomac River and Chesapeake Bay— threatens to undo decades of restoration progress.”

Meanwhile, the river is seeing more common game fish like shad and white perch. They aren’t without risk, however: “Populations of non-native northern snakehead fish and blue catfish are rapidly growing and expanding into new areas of the Potomac. Their impact on the river’s ecosystem is not fully known at this time, but there is concern they could harm other fish populations through competition and predation.”

At the same time, the District Department of Energy & Environment advises against eating some of the fish from the river due to polychlorinated biphenyl (PCB) levels. (Businesses and restaurants have taken note.)

The authors are concerned in particular about meager recovery rates for “underwater grasses, habitat, and water clarity” in the Potomac. Tidal-water quality, for example” has flatlined during the past several years.

You can read the conservancy’s the full report here.

Update 12:00 p.m.: DOEE Director Tommy Wells provided the following statement about the report:

“The Potomac Conservancy report illustrates how our citywide efforts to restore and protect our waterways are beginning to pay off. Treating our local rivers like major city assets has been good for the Chesapeake Bay and great for the District of Columbia. DOEE’s shad restoration project has successfully exceeded its goals and we continue to see an increase in recreational fishing. Our rivers play a crucial role in sustaining local wildlife and we’re seeing the return of important wildlife species, including bald eagles raising their young on the banks of the Anacostia River and ravens nesting along the Potomac River for the first time in more than a century. There is still considerable work to be done, but we remain committed to these efforts to ensure our waterways are fishable and swimmable for generations to come.”