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Underwater Bay Grass Abundance (Baywide)

In 2013, there were an estimated 59,927 acres of underwater grasses in the Chesapeake Bay. This marks an increase of almost 12,000 acres since 2012 and an achievement of 32 percent of the 185,000-acre goal.

Bay Grasses (SAV) Restoration Goal Achievement: Single Best Year 2011-2013

Map: Bay Grasses (SAV) Restoration Goal Achievement: Single Best Year 2011-2013

Date created: Apr 03 2014 / Download

This map shows progress toward achieving the Chesapeake Bay Program segment-specific underwater bay grass restoration goals. It is based on the single best year of acreage as observed through the most recent three years of data from the Chesapeake Bay underwater bay grasses aerial survey.

April 22, 2011

Bay grasses, also known as submerged aquatic vegetation, are an integral part of the Chesapeake Bay ecosystem. Lee Karrh from the Maryland Department of Natural Resources (DNR) explains what bay grasses need to grow and why their survival is important to Bay critters.

April 22, 2011

What is submerged aquatic vegetation, and why is it important to the Chesapeake Bay?  Commonly known as “bay grasses” they among the most critical inhabitants of the Bay’s ecosystem.  Find out more about submerged aquatic vegetation, and see what people around Baltimore’s Belvedere Square had to say about it.


Restoring underwater grasses to the rivers, streams and shallow waters of the Chesapeake Bay will dramatically improve the Bay ecosystem. Grass beds provide food and shelter to fish, crustaceans and other species, add oxygen to the water, absorb nutrient pollution, reduce shoreline erosion and help suspended particles of sediment settle to the bottom.

Underwater grasses—also known as submerged aquatic vegetation or SAV—are sensitive to pollution but quick to respond to improvements in water quality. This means their abundance is a good indicator of Bay health. As pollution declines and water clarity improves, scientists expect underwater grasses to expand.


In 2014, the Chesapeake Bay Program renewed its goal to achieve and sustain 185,000 acres of underwater grasses in the Chesapeake Bay. Progress toward this goal will be measured against a target of 90,000 acres by 2017 and 130,000 acres by 2025. 

Past goals

In 1993, the Bay Program set a goal to restore 114,000 acres of underwater grasses to the Bay. Based on recovery rates at the time, partners expected to achieve this goal by 2005.

In 2000, the Bay Program recommitted to this 114,000-acre goal but agreed to “revise… restoration goals and strategies to reflect historic [underwater grass] abundance, measured as acreage and density from the 1930s to the present.” In 2003, the Bay Program adopted the Strategy to Accelerate the Protection and Restoration of Submerged Aquatic Vegetation in the Chesapeake Bay, which set a new Bay-wide restoration goal of 185,000 acres by 2010.

Historic data

Reviews of photographs from a number of sites dating back to 1937 suggest that close to 200,000 acres of underwater grasses may have once grown along the shorelines of the Chesapeake Bay. By 1984, nutrient and sediment pollution had weakened or eliminated grass beds in many areas, contributing to a Bay-wide SAV decline.

Long-term trend (1984-2013)

Between 1984 and 2013, underwater grass abundance increased from 38,958 acres to 59,927 acres. Abundance averaged 65,468 acres and ranged from its 1984 low to a high of 89,659 acres in 2002.

Short-term trend (2004-2013)

Between 2004 and 2013, underwater grass abundance decreased from 72,945 acres to 59,927 acres. Abundance averaged 68,893 acres and ranged from 48,195 acres in 2012 to 85,914 acres in 2009.

Change from previous year (2012-2013)

Between 2012 and 2013, underwater grass abundance increased 24 percent from 48,195 acres to 59,927 acres.

Additional Information

Collecting data

This data is collected through an aerial survey flown from late spring to early fall by researchers with the Virginia Institute of Marine Science (VIMS). VIMS processes the photography in fall and winter and provides preliminary area totals the following spring. Visit the VIMS SAV website for more information about the survey or for segment-specific survey results.

Reporting data

For almost 30 years, underwater grass acreage was reported in three geographic zones. Zone 1 was above the Chesapeake Bay Bridge, Zone 2 covered the area between the Bay Bridge and the mouth of the Potomac River and Zone 3 covered the area between the mouth of the Potomac and the mouth of the Bay. But these zones span a wide range of salinities and do not account for salinity-related changes in underwater grass communities. Because the makeup of grass communities changes as salinity increases—and because these communities respond differently to heat, drought, storms and other events—it makes more ecological sense to report underwater grass acreage by salinity zone than by geographic zone. This can also help scientists find patterns in how underwater grasses are growing.

To see underwater grass abundance reported in these salinity zones, visit our Underwater Bay Grass Abundance in Four Salinity Zones indicator.

Source of Data

Virginia Institute of Marine Science

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