Chesapeake Bay health grade dips after hottest year on record and extreme rainfall patterns

ANNAPOLIS, Md. (AP) — The health of the Chesapeake Bay declined in an annual report card on the nation’s largest estuary released Tuesday, with scientists noting the effect of extreme rainfall patterns during the hottest year on record.

The University of Maryland Center for Environmental Science gave the bay a C grade in its report card. That compares to a C-plus grade the bay received last year, which was the highest grade it had received since 2002.

“There was a substantial upturn in the overall Bay Health score in 2024, and it came down a little this year,” said Heath Kelsey, director of UMCES Integration and Application Network. “Over the long term, though, there is still an improving trend from the 1980s until now. We think extreme weather may have had some impact on the scores this year.”

The report noted that last year was the hottest year on record, with extreme rainfall patterns.

“While parts of the watershed experienced drought, brief but intense downpours can cause water to flow over the ground rather than soak into it, increasing the fertilizer, dirt, and debris carried into waterways,” the report said.

Bill Dennison, vice president for Science Application at UMCES, said the changing climate is definitely having an effect on the bay.

“One of the things that we saw in Maryland, in particular, was a prolonged summer drought — not so much spring, but a summer drought — punctuated by these extreme runoff events,” Dennison said. “So what was happening was that the crops didn’t have enough water, so they’re not soaking up the nutrients.”

As a result, when it did rain, there were excess nutrients, like nitrogen and phosphorus, that were flowing into the bay, Dennison said.

“Now sadly, this is kind of our future,” Dennison said at a news conference at the Annapolis Maritime Museum near the bay. “This is the kind of weather patterns that are starting to become more common, which is drought punctuated by extreme events.”

Warmer weather winters and higher temperatures mean less oxygen in the water for aquatic life, stressing fish and shellfish, Dennison added.

“So these are some of the things that we have to overcome and build more resilience into our system,” Dennison said.

Despite the grade drop, the report cited long-term improvements in dissolved oxygen in the bay’s waters. That’s the amount of oxygen present in the water that is needed to support bay aquatic life.

The report also noted long-term improvements in aquatic grasses, which provide habitat and food for various species, improve water quality and protect shorelines from erosion.

Phosphorus and nitrogen levels also have improved in the long-term in another positive sign. While they are needed by the bay’s organisms, excessive nitrogen and phosphorus degrade the bay’s water quality. Excess nitrogen and phosphorus fuel algal blooms that can cloud the water and block sunlight from reaching underwater grasses.

Water clarity and chlorophyll-a scores, however, have declining long-term trends, the report said. Chlorophyll-a in the bay is an indicator of phytoplankton abundance and water quality.

Improving trends can be attributed to management and restoration efforts at the regional, state, and local levels, the report said. Regionally, wastewater treatment plants have been upgraded and programs have been put in place to reduce nutrient and sediment input.

The health of the bay is a reflection of what’s happening across its six-state watershed, which includes Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia along with the District of Columbia.

UMCES, which is marking its 100th anniversary, also provides a grade for the overall watershed health in its report card. It gave the watershed a grade of C-plus. The watershed health grade includes ecological, societal and economic indicators.

The most concerning societal indicator was heat vulnerability, the report said, noting communities may be under heat stress due to hotter air temperatures, less tree canopy cover, and more paved surfaces.