Recent Progress: Increase

According to data from the Virginia Institute of Marine Science (VIMS), 79,716 acres of underwater grasses were mapped in the Chesapeake Bay and its tributaries in 2023. This is 61% of the Chesapeake Bay Program’s 2025 restoration target of 130,000 acres and 45% of the partnership’s 185,000-acre goal. However, these 79,716 acres are considered an underestimate because security restrictions prevented a portion of the Potomac River, which previously mapped 3,703 acres of SAV in 2022, from being fully mapped in 2023. Based on 2022 data for the unmapped areas, it is estimated that the Bay may have supported 83,419 acres of SAV in 2023, representing about 8% increase from the 2022 total of 77,425 acres and 64% of the 2025 restoration target. This is an 114% increase from the first SAV survey in 1984 and indicates an increase in progress for this outcome. 

Outlook: Off Course

The Submerged Aquatic Vegetation (SAV) Outcome is off course. The increase from 2021 to 2023 is positive, but these gains don’t yet offset the major decline of underwater grasses observed in 2019. Additional years of positive trajectory will help clarify whether the gains over the past few years represent a positive trend toward higher levels of SAV across the Bay, but it is unlikely that the 2025 goal of 130,000 acres will be met.

Submerged Aquatic Vegetation (SAV) Abundance (1984-2023) ^‍‍

*Estimated Additional Acreage: Factors such as adverse weather conditions, water clarity, or security restrictions over military air space prevented researchers from collecting aerial imagery. For these unmapped areas, estimates of SAV acreage are based on the prior year’s survey. Data were not collected in 1988.

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Submerged Aquatic Vegetation (SAV) Abundance (2010-2023) ^‍‍

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‍Data (.xlsx) ‍Methods (.docx) ‍Image (.png)

In 2023, the Bay’s Tidal Fresh, mesohaline (moderately salty) and polyhaline (very salty) salinity zones showed increases in SAV. The oligohaline (slightly salty) zone showed a large decrease in reported SAV, however this decrease is attributed to the partial mapping of the zone in 2023, which was due to security restrictions of aerial monitoring. 

• Tidal Fresh Zone: Underwater grass beds increased 3% from 19,185 acres in 2022 to an estimated 19,823 acres in 2023. This represents a 96% achievement of the region’s 20,602-acre goal.
• Oligohaline Zone (slightly salty): Reported underwater grass beds dropped 54% from 7,145 acres to an estimated 3,422 acres, a 33% achievement of the region’s 10,334-acre goal. This was impacted by the partial mapping of this zone in 2023 as well as losses in the middle Potomac River, the Gunpowder River and other rivers in the upper Bay. 
• Mesohaline Zone (moderately salty): Underwater grass beds increased 21% from 30,932 acres to 38,371 acres, a 30% achievement of the region’s 120,306-acre goal. 
• Polyhaline Zone (very salty): Underwater grass beds increased 12% from 19,200 acres to 21,803, a 65% achievement of the region’s 33,647-acre goal. This is the most SAV reported in the Polyhaline zone since 1997.

Experts attribute the increases in the polyhaline and mesohaline zones to recovery from the SAV crash in 2019. The losses in 2019 were largely due to declines in widgeon grass, a species whose abundance can rise and fall from year to year in response to changes in water quality and weather conditions. For example, in 2018, widgeon grass increased in the mesohaline and northern polyhaline salinity zones, but subsequently declined after high precipitation in 2018 and 2019, which mirrors a similar rapid increase in 2001 and 2002 that was followed by about a 50% decline in 2003.

The expansion in the polyhaline zone is attributable to a La Nina climate cycle which has resulted in cooler summers, benefiting eelgrass. The primary losses in the oligohaline were concentrated in a small area: the Gunpowder River, the Middle River and the adjacent central channel of the Bay. These declines may have been influenced by phytoplankton blooms and suspended sediment observed in those areas in the spring and summer of 2022.

In 2023, high density beds accounted for 62% of the total acreage, which is 4% higher than in 2022. The density classifications for the beds in 2023 are as follows:

• 2% of the beds had densities of <10% (Class 1)
• 14% of the beds had densities of 10-40% (Class 2)
• 23% of the beds had densities of 40 -70% (Class 3)
• 62% of the beds had densities of 70-100% (Class 4)

Underwater grass beds are critical to the Chesapeake Bay ecosystem. They provide food and shelter to fish and wildlife, sequester carbon and buffer coastal acidification, add oxygen to the water, absorb nutrient pollution, reduce shoreline erosion and help suspended particles of sediment settle to the bottom. Because they are sensitive to pollution but quick to respond to improvements in water quality, underwater grass abundance is a good indicator of the Bay’s health. 

Review of photographic evidence from several sites dating back to 1937 suggests that between 200,000 to 600,000 acres of SAV may have grown along the shoreline of the Bay. However, by 1984, that number had fallen to a low of about 38,000 acres. Research has shown that nutrient reductions made under the Chesapeake Bay Total Maximum Daily Load (Bay TMDL) have played a critical role in the overall underwater grass recovery documented since the Bay-wide aerial survey began in 1984. But these nutrient reductions have not been adequate to improve water clarity to the extent necessary for SAV goal attainment. Continued and accelerated nutrient reductions are necessary to facilitate future SAV recovery. Climate change and sediment loading from shoreline alteration and land use changes will also continue to impact restoration success. Thus education, outreach, regulation, investment and application of restoration science will continue to be critical to managing climate and societal stressors, alongside accelerated nutrient reductions.

More information about underwater grass abundance in the Chesapeake Bay can be found on the Virginia Institute of Marine Science (VIMS) website.

Learn About Factors Influencing Progress

To achieve this outcome, Chesapeake Bay Program partners have committed to:

• Supporting efforts to conserve and restore current and future underwater grass habitat and habitat conditions.
• Protecting existing and recovering underwater grasses.
• Restoring underwater grasses.
• Enhancing underwater grass research and monitoring.
• Enhancing community involvement, education and outreach.

These partners will also collaborate with the work being done to achieve the 2025 Watershed Implementation Plans (WIPs) and Water Quality Standards Attainment and Monitoring outcomes.

Monitoring and assessing progress toward the outcome will occur through analysis of data related to underwater grass distribution and abundance.

As part of the Chesapeake Bay Program’s partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in December of 2023.

Download Management Strategy (.pdf)

Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.

Ongoing

• Monitoring submerged aquatic vegetation throughout the Chesapeake Bay and its tidal tributaries through the Bay-wide aerial survey, the Chesapeake Bay SAV Watchers program, and the SAV Sentinel Site Program.
• Tracking advancements in the scientific understanding of underwater grass biology, ecology, genetics, restoration and other related topics.
• Encouraging local, state and federal partners to manage those invasive species that are detrimental to underwater grasses.
• Supporting the Water Quality Goal Implementation Team (GIT) in its efforts to achieve water clarity standards in areas designated for submerged aquatic vegetation use.
• Convening quarterly, in-person meetings of the Submerged Aquatic Vegetation Workgroup to discuss priorities, review status updates and implement work plan actions.
• Working to review and implement appropriate recommendations from the 2019 SAV Regulatory Review that protect underwater grasses in the Chesapeake Bay.
• Continuing efforts to expand SAV restoration activities: establish underwater grass beds through direct seeding where they are not recovering naturally and adding diversity to grass beds that have already recovered; use these restoration activities to engage and educate citizen volunteers and further our understanding of site selection criteria; distribute the recently completed SAV Restoration Guide; work with permitting agencies to ensure SAV restoration activities are permitted during appropriate growing conditions and to prevent over-harvesting from donor aquatic grass beds.
• Encouraging local, state and federal partners to consider and promote the habitat benefits and ecosystem services of underwater grasses.
• Assessing and promoting the use of best management practices (BMPs) that benefit the persistence and recovery of underwater grass beds.
• Determining the local effect of flow and stormwater runoff on SAV density and acreage and options for targeting best management practices (BMPs) that would protect priority SAV areas.
• Reviewing potential opportunities to create a Chesapeake Bay SAV nursery or SAV nursery network.
• Developing a communication strategy that enhances the public's knowledge of and appreciation for SAV in Chesapeake Bay.

Recently Completed

2022-2023

• Held Scientific and Technical Advisory Committee (STAC) workshops on rising temperatures in the Bay, including evaluating the potential impact on SAV restoration and its ability to provide relevant ecosystem services.
• Completed and published the results of the GIT-funded SAV/Climate Modeling Project to evaluate the attainability of SAV restoration targets in the face of climate change as well as a report on the STAC workshop and management recommendations.
• Completed the development and publication of the SAV Monitoring Program webpages on Chesapeakebay.net.
• Identified and prioritized an updated list of SAV science and research needs.
• Worked with the Bay Program partners to identify funding opportunities to support the continued exploration of satellite imagery and the development of algorithms and workflows to automate SAV detection and quantification.
• Continued implementation of the SAV Watchers Program and worked to identify funding opportunities to ensure the long-term stability of the SAV Watchers Program.
• Finalized the SAV Sentinel Site monitoring protocol and developed an implementation plan for the SAV Sentinel Site Program that includes identification and commitment from site adopters.

Learn About Logic & Action Plan

The Submerged Aquatic Vegetation Workgroup, which is part of the Vital Habitats Goal Implementation Team leads the effort to achieve this outcome. It works in partnership with the Sustainable Fisheries and Water Quality goal implementation teams.

Participating partners include:

• Maryland Department of Natural Resources (State of Maryland)
• Maryland Department of the Environment (State of Maryland)
• Virginia Coastal Zone Management Program
• Virginia Department of Environmental Quality (Commonwealth of Virginia)
• Virginia Marine Resource Commission
• D.C.’s Department of Energy and Environment (District of Columbia)
• U.S Environmental Protection Agency
• Virginia Institute of Marine Science (Commonwealth of Virginia)
• University of Maryland Center for Environmental Science (State of Maryland)
• St. Mary’s College of Maryland
• Old Dominion University
• Smithsonian Environmental Research Center
• Tetra Tech, Inc.
• Chesapeake Bay Foundation
• The Nature Conservancy
• U.S. Fish and Wildlife Service
• U.S. Geological Survey
• National Oceanic and Atmospheric Administration
• U.S Army Corps of Engineers
• U.S. Fish and Wildlife Service
• National Oceanic and Atmospheric Administration
• U.S. Geological Survey
• U.S. Army Corps of Engineers
• Local Riverkeepers and Watershed Organizations