Chesapeake Bay underwater grasses reach highest level since 2018

Seagrass such as this eelgrass meadow provides foundational habitat supporting many species in the Chesapeake Bay. Photo by Alyson Hall.

Underwater grasses in the Chesapeake Bay increased 7% last year, reaching their highest Bay-wide level since 2018 and approaching an important regional restoration goal.

Researchers at William & Mary’s Virginia Institute of Marine Science and Batten School of Coastal & Marine Sciences recorded an estimated 89,385 acres of submerged aquatic vegetation in the Bay and its tidal tributaries in 2025. That was an increase of 6,134 acres from 2024.

The total is just short of the Chesapeake Bay Watershed Agreement’s interim goal of 90,000 acres by 2030. It represents about 45% of the long-term restoration goal of 196,600 acres.

“This year’s survey demonstrates both that we’re moving in the right direction and that there is a lot of complexity in Chesapeake Bay underwater grass communities,” said Christopher J. Patrick, director of the VIMS submerged aquatic vegetation program.

Much of the growth occurred in the saltier portions of the Bay, including waters near its mouth. The Polyhaline Zone, which contains the Bay’s saltiest waters, increased from 25,266 acres in 2024 to an estimated 28,142 acres in 2025. The region set a new record for submerged vegetation coverage for the second consecutive year.

The moderately salty Mesohaline Zone grew nearly 15%, increasing from 33,033 acres to approximately 37,879 acres.

Researchers said sustained improvements in water clarity in the lower Bay are helping eelgrass meadows expand in size and into deeper water. Widgeon grass is also continuing to recover in the middle Bay after exceptionally wet conditions caused a major decline in 2018.

“It’s been remarkable to watch how fast the lower Bay meadows are expanding right now,” Patrick said. “It’s another example of how rapidly seagrass can recover when conditions are right.”

The Bay-wide improvement was not uniform. Underwater grass coverage in freshwater rivers and embayments declined from 20,221 acres to an estimated 18,653 acres. Significant losses were observed in several Virginia tributaries, including portions of the upper Rappahannock River.

Researchers attributed much of that decline to reductions in hydrilla, also known as water thyme, an invasive aquatic plant that has expanded and contracted in several river systems. Coverage in the slightly salty Oligohaline Zone remained relatively stable at slightly more than 4,700 acres.

Underwater grasses provide habitat for fish, blue crabs, waterfowl and other wildlife. The plants also absorb nutrients, stabilize sediment, reduce shoreline erosion, produce oxygen and help improve water quality.

Scientists consider the grasses one of the Bay’s most sensitive indicators of environmental health because they respond quickly to changes in water clarity, rainfall, salinity and nutrient levels.

Historical evidence suggests the Chesapeake Bay once contained between 200,000 and 600,000 acres of underwater grasses. When systematic monitoring began in 1984, only about 39,000 acres remained.

Coverage has more than doubled since then, with researchers attributing part of the recovery to reductions in nutrient pollution throughout the watershed.

Interactive maps and additional survey information are available through the VIMS Submerged Aquatic Vegetation Program. More information about Bay restoration goals is available from the Chesapeake Bay Program.