Heath Kelsey and Bill Dennison, both of the University for Maryland Center for Environmental Science, talk about the findings in the center's 2025 Chesapeake Bay report card.
The Chesapeake Bay’s ecological health declined in 2024 as extreme heat, rainfall and drought wreaked havoc across the estuary’s watershed, according to the latest annual report card from the University of Maryland Center for Environmental Science. Experts worry it may be a sign of things to come.
The grade for the Bay’s aquatic health slipped from a C+ in 2023 to a C last year, dropping 5 percentage points to an overall score of 50%, UMCES reported.
“A changing climate is definitely affecting the Bay,” said UMCES vice president Bill Dennison. “These are the kinds of weather patterns that are starting to become more common … drought punctuated by severe weather events.”
The announcement of the decline comes at a precarious moment for Bay advocates.
State and federal officials are trying to complete by the end of the year a top-to-bottom revision of the regional agreement that guides the restoration. And the second Trump administration, while vowing not to cut the Chesapeake Bay Program at the U.S. Environmental Protection Agency, is proposing widespread cutbacks to other programs that support the 42-year-old cleanup effort.
“The extreme weather of 2024 is not an anomaly — it’s a warning,” said Chesapeake Bay Foundation President and CEO Hilary Harp Falk in a statement. “Climate change is accelerating, and with it comes more flooding, pollution and ecological stress. The Trump administration’s proposed budget cuts threaten the world-class science and partnership at the heart of the effort.”
The water quality in the Bay and throughout its drainage basin can vary widely from year to year because of differences in weather, Dennison said June 10 at an event unveiling the report card at the Annapolis Maritime Museum.
The lower score wasn’t unexpected. Last summer’s weather conditions – which went from too wet in the beginning to too dry at the end, and hotter overall — were a recipe for sparking a downturn in the system’s health, scientists say.
“What was happening was the crops didn’t have enough water, so they were not soaking up the nutrients,” Dennison explained. “So, when it did rain, there were excess nutrients running into the Bay.”
The weather trend from previous decades is expected to continue: wetter, with more rain coming in extreme storms.
An overabundance of nutrients presents a feast to algae blooms. The microscopic organisms multiply by the billions and consume oxygen in the water when they die off, leading to “dead zones” in the Bay’s deepest reaches. There, the nearly oxygen-free environment smothers any life that can’t flee fast enough.
Last year’s record heat further inflamed the situation, Dennison said. That’s because warmer water holds less oxygen than cooler water, and the hotter temperatures boost the temperature stratification of the Bay’s water column. That, in turn, prevents the layers from mixing, trapping the oxygen-starved waters at the bottom.
“Now, sadly, this is our future,” he said, referring to the damage from climate change.
Trying to reduce nutrient and sediment runoff while the climate trends hotter and stormier is “like trying to walk up a down escalator,” said U.S. Senator Chris Van Hollen in taped remarks. “The only thing to keep things from getting worse is to walk faster.”
An algal bloom plagues warm shallow water in Maryland’s Choptank River.
Despite last year’s drop-off, the Bay’s health since the 1980s has gradually improved, rising from an average score of 44.4 over the five report cards released from 1986-1991 to 50.2 over the last five. Scores for dissolved oxygen, submerged aquatic grasses, the nutrients phosphorus and nitrogen show improving trends while scores for chlorophyl and water clarity have declined over that time.
The report card attributes those improvements largely to restoration efforts, such as upgrades to wastewater treatment plants, oyster replenishment and aquatic grass plantings.
The report carves up the Bay and its tributaries into 15 segments. Six of those had better health scores in 2024: the Elizabeth, James and Patapsco/Back rivers as well as the upper Western Shore, the upper Bay mainstem and the lower Bay mainstem.
Josh Kurtz, Secretary of the Maryland Department of Natural Resources, speaks during the unveiling of the 2025 Chesapeake Bay report card produced by the University of Maryland.
The best score belonged to the lower Bay, which received a B. Dennison traced that to the tidal exchange with the nearby Atlantic Ocean and to improvements in Virginia’s James River. He applauded the James River Association, one of the lower Bay’s largest environmental groups, for the efforts that won it the Thiess International Riverprize in 2019.
Meanwhile, the letter grade for the Chesapeake’s “watershed health,” as opposed to its aquatic health, notched upward to a C+ in 2024, raising its score from 52% to 57%. That score refers to the health of the 64,000-square-mile watershed as a whole and considers ecological, societal and economic indicators. For specific regions, scores ranged from 42% in the Choptank River watershed on Maryland’s Eastern Shore to 61% along the upper James.
The UMCES report card has long coexisted with another Baywide health assessment independently authored by the Chesapeake Bay Foundation, the largest nonprofit dedicated to protecting and restoring the Bay watershed. UMCES officials announced at the Annapolis event that the two entities plan to work together on future report cards.
“It will reduce the confusion of having two separate report cards and slightly different messaging,” said Heath Kelsey, director of UMCES Integration and Application Network, “but we’re still working out the details.”
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