A mix of wild celery (Vallisneria americana) and water stargrass (Heteranthera dubia), both freshwater underwater grasses. Photo by Brooke Landry, Maryland Department of Natural Resources.
Underwater grass abundance in Maryland’s portion of the Chesapeake Bay – a key indicator of water quality – fell from 38,188 acres in 2023 to 36,794 acres in 2024, according to data reviewed by the Maryland Department of Natural Resources. This acreage remains short of the state’s 2025 restoration goal of 79,800 acres.
The annual survey of submerged aquatic vegetation (SAV) was conducted by the Virginia Institute of Marine Science between May and October 2024. The Bay was fully mapped in 2024.
In Maryland, despite an overall loss of underwater grass acreage, freshwater SAV populations did well in 2024 and all or part of five rivers surpassed their restoration goals.
“The resilience we’re seeing in freshwater SAV beds this year is encouraging and reflects years of targeted restoration, outreach, and monitoring,” DNR’s SAV Program Chief Brooke Landry said. “But sharp declines in widgeon grass across the mid-Bay are concerning, especially given how quickly this species can respond to changes in water quality. These shifts underscore the need for sustained action to improve local conditions and maintain the habitats that so many Bay species rely on.”
Submerged aquatic vegetation (SAV) plays a critical role in the health of the Chesapeake Bay ecosystem. Commonly known as bay grasses, these underwater plants provide essential habitat and nursery grounds for fish, blue crabs, and other aquatic life, while also improving water quality by absorbing excess nutrients, stabilizing sediments, and slowing shoreline erosion. SAV also helps buffer the Bay against the impacts of climate change by sequestering carbon and reducing acidity in the water. Because of these wide-ranging benefits, the abundance and distribution of SAV is a key indicator of the Bay’s overall health and resilience.
In the 2024 survey, rivers surpassing their restoration goals include the North East River at 165%, the Bush River at 133%, the Back River at 275%, the upper Chester River at 274%, and Mattawoman Creek on the Potomac at 110%.
Two additional segments reached 75 percent or more of their restoration goals. The northern Chesapeake Bay segment 2, which encompasses the Susquehanna Flats, reached 90% of its 12,149-acre SAV goal and the northern Chesapeake Bay segment 1, which is the area just south of the Susquehanna Flats, reached 88% of its 754-acre SAV goal.
Several other rivers on the upper western shore that support freshwater SAV populations also began to recover from major losses in 2022 and 2023, with SAV gains in the Gunpowder and Middle Rivers as well as in the shallow waters of the Upper Chesapeake Bay mainstem. Freshwater SAV populations in the Bay benefit from high species diversity, which increases their resilience and enables them to recover from loss more effectively.
The expanse of freshwater SAV populations was overshadowed by the loss of grasses in the mid-Bay, which supports underwater vegetation acclimated to slightly saltier conditions, like widgeon grass (Ruppia maritima) and sago pondweed (Stuckenia pectinata). Substantial losses were observed in Eastern Bay (-36%), at the mouth of the Choptank River (-41%), in the Little Choptank River (-83%), in Fishing Bay (-83%), and in Tangier Sound (-8%).
Widgeon grass is the most widespread SAV species in the Bay due to its broad salinity tolerance. However, widgeon grass is sensitive to abrupt changes in salinity and water quality, which made it susceptible to loss after storms that delivered fresh, turbid water during the spring and early summer of 2024.
Additionally, reports from the department’s SAV Program suggest that widgeon grass populations throughout Maryland’s tributaries appear to have produced fewer seeds in 2023 than normal. Seeds are an important component of this species’ ability to expand each growing season, and low widgeon grass seed production in 2023 combined with rapidly changing conditions during the early part of the growing season in 2024 may be the cause of the reduced SAV acres. Department scientists are looking into the possibility that widgeon grass seed production is impacted by abnormally high water temperatures.
Protecting and restoring submerged aquatic vegetation is essential to the long-term health and resilience of Chesapeake Bay. These underwater grasses support a rich diversity of life, improve water quality, and help the Bay adapt to a changing climate. As the department continues to track SAV trends and respond to emerging challenges, collective action is key to ensuring that these vital habitats—and the benefits they provide—are sustained for generations to come.
