One year after the Chesapeake Bay earned its highest ever grade of a C+, the estuary’s health slipped back to a C in its latest report card.

The University of Maryland Center for Environmental Science gave the Chesapeake Bay a score of 50% in a new annual assessment released Tuesday, reflecting poorer performance in almost every environmental category. Considered a “moderate” score, this year’s score marks a 5-point backslide from the bay’s record-setting grade a year ago.

From year to year, the bay’s health can swing depending on changes in the climate, and scientists said the overall picture is still improving, even if this year’s grade marks a step back.

Last year’s weather wasn’t good for the bay, said Bill Dennison, UMCES’ vice president for science application, who helped lead the new assessment.

“It was too wet, then it was too dry and it was always too hot,” Dennison said.

A four-decade campaign to restore the Chesapeake Bay has been hampered by climbing population across its watershed, stubborn agricultural pollution and — increasingly — the changing climate.

Despite those factors, said Heath Kelsey, UMCES’ director of the integration and application network, the bay’s health is improving, slowly but steadily. Kelsey said he hopes the bay can routinely score a C+ in the not-so-distant future.

Even so, the regionwide effort to clean up the Chesapeake Bay missed most of its goals ahead of a much-anticipated 2025 deadline. And though President Donald Trump hasn’t recommended defunding the restoration — as he did in his previous term — the future of federal support is shaky.

The annual report card weighs factors like the health of underwater grasses and the concentrations of nitrogen and phosphorous pollution, nutrients breeding “dead zones” that starve underwater life of oxygen.

According to the new report, the health of every region in the bay is either holding its ground or improving, except for one: the Eastern Shore.

Tributaries north of the Eastern Shore’s Choptank River received a D in the new report card, part of a worsening trend Dennison described as “a little bit of an enigma.” Farms are certainly a driving factor, but Dennison said regulators and scientists have implemented steps to reform agricultural practices across the watershed, and it’s not clear why the results have lagged on the Delmarva Peninsula.

“We’ve got a problem on the Eastern Shore,” he said. “We’ve known it for some time.”

On the other hand, Dennison and Kelsey each described the Patapsco River and its Baltimore harbor as bright spots.

Once an industrial dumping ground and now a major population center, the Baltimore harbor has long been the most polluted corner of the estuary. This year, the Patapsco River region and the lower western shore recorded the lowest scores across the Chesapeake, each drawing “poor” 27% grades in their health assessment, followed closely by the Patuxent River at 28%.

“It’s always been the worst, but it’s not going to continue to be the worst.”

— Bill Dennison, UMCES’ vice president for science application

But as regulators and Baltimore leaders have tightened the screws on their wastewater treatment plants, the urban harbor has made progress.

“It’s always been the worst, but it’s not going to continue to be the worst,” Dennison said of the Patapsco.

Maryland leaders touted the state’s own work to stem pollution at Tuesday’s announcement at the Annapolis Maritime Museum.

Natural Resources Secretary Josh Kurtz said Trump administration cuts could stress underwater grasses and an already struggling blue crab population, in particular. But he also emphasized recent Maryland policies to fund tributary cleanup and incentivize friendlier practices by farms and businesses.

Meanwhile, officials and scientists pointed to headway at the north end of the bay, where the Susquehanna River empties out of Pennsylvania.

Pennsylvania farms have long been blamed for the Chesapeake’s ailing condition, but in the 2024 assessment, the region closest to the Susquehanna ranked second only to the southern end, where the Atlantic Ocean mixes with the bay.

UMCES has been grading Chesapeake health for two decades, and this year the research institute celebrates its 100th anniversary. To commemorate the occasion, scientists also released a retrospective report card, grading the bay’s health in 1925.

Familiar issues like wastewater pollution, runoff from cities, oxygen dead zones and global warming were still decades away. In UMCES’s early days, the bay’s biggest worries included overfishing and a dwindling diamondback terrapin population.

The overall verdict for the Chesapeake Bay of 100 years ago? A “respectable” B.