According to preliminary data from the Virginia Institute of Marine Science (VIMS), 91,559 acres of underwater grasses were mapped in the Chesapeake Bay in 2018. However, 22 percent of the Bay was not fully mapped due to prolonged turbidity, weather conditions and security restrictions. Using 2017 levels for the unmapped areas, it is estimated that the Bay may have supported 108,960 acres of SAV in 2018. This is a 4 percent increase from 2017 figures and 59 percent of the partnership’s 185,000-acre goal.

Interactive Chart

Submerged Aquatic Vegetation (SAV) Abundance (1984-2018)

Interactive Map

Submerged Aquatic Vegetation (SAV) Abundance (2010-2018)

In 2018, adverse weather conditions, poor water clarity and security restrictions prevented researchers from collecting aerial imagery for a portion of tidal fresh and mesohaline Potomac River; the Susquehanna, Mattaponi, Middle, Choptank, and Honga rivers; and Fishing Bay. Satellite imagery was acquired to address these gaps, but was not sufficient to cover the entire missing area, approximately, 22 percent of the 2017 Bay total. In 2018, high density beds accounted for 61 percent of the total acreage, which is 17 percent higher than 2017.

While the overall trend is upward, the magnitude of changes from 2017 and 2018 varied by salinity zone:

  • Tidal Fresh Zone: Underwater grass beds decreased from an estimated 19,903 acres to 19,012* acres, a 4.5 percent decrease and 92 percent achievement of the region’s 20,602-acre goal.
  • Oligohaline Zone (slightly salty): Underwater grass beds decreased from an estimated 8,389 acres to 7,687* acres, an 8.5 percent decrease and 74 percent achievement of the region’s 10,334-acre goal.
  • Mesohaline Zone (moderately salty): Underwater grass beds increased from an estimated 61,350 acres to 64,281* acres, a 5 percent increase and 53 percent achievement of the region’s 120,306-acre goal.
  • Polyhaline Zone (very salty): Underwater grass beds increased from an estimated 15,251 acres to 17,980 acres, an 18 percent increase and 53 percent achievement of the region’s 33,647-acre goal.

*These areas were not fully mapped in 2018

Experts attribute the 2018 increases in the mesohaline and polyhaline zones to a continuing rapid expansion of widgeon grass. Because widgeon grass is a “boom and bust” species whose abundance can rise and fall from year to year, a widgeon-dominant spike is not guaranteed to persist in future seasons.

Underwater grass beds are critical to the Chesapeake Bay ecosystem. They provide food and shelter to fish and wildlife, sequester carbon, 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. Before Europeans colonized the region, up to 600,000 acres of underwater grasses grew along the shorelines of the Bay and its tributaries. By the mid 1980s, nutrient and sediment pollution had weakened or eliminated many of these grass beds. While climate change, shoreline hardening and stressors that reduce water clarity will continue to impact our restoration success, many of these stressors can be managed with on-the-ground efforts to reduce pollution and research has shown that nutrient reductions made under the Chesapeake Bay Total Maximum Daily Load (Bay TMDL) have played a critical role in underwater grass recovery.

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

Management Strategy

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

  • Supporting efforts to restore water clarity in the Chesapeake Bay;
  • Protecting existing underwater grasses in the Chesapeake Bay;
  • Restoring underwater grasses in the Chesapeake Bay; and
  • Enhancing submerged aquatic vegetation research, citizen involvement and public education and outreach in the watershed.

These partners will also collaborate with the work being done to achieve the 2017 and 2025 Watershed Implementation Plans (WIPs) and Water Quality Standards Attainment and Monitoring outcomes.

Monitoring and assessing progress toward the outcome will occur through 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 November of 2019.

Logic & Action Plan

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

Participating Partners

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)
  • University of Maryland Center for Environmental Science (State of Maryland)
  • Virginia Institute of Marine Science (Commonwealth of Virginia)
  • Virginia Department of the Environmental Quality (State of Virginia)
  • Virginia Marine Resources Commission
  • Department of Energy and Environment (District of Columbia)
  • National Oceanic and Atmospheric Administration
  • U.S. Army Corps of Engineers
  • U.S. Environmental Protection Agency
  • U.S. Fish and Wildlife Service
  • U.S. Geological Survey