Underwater grasses, also known as submerged aquatic vegetation (SAV), are seen at Round Bay on the Severn River in Anne Arundel County, Md., on Aug. 26, 2019. (Image by Will Parson/Chesapeake Bay Program)

One of the most important species to the Chesapeake Bay ecosystem is also its most overlooked. While blue crabs, rockfish or waterfowl may immediately come to mind, none of these creatures are able to survive without the help of underwater grasses. Bay grasses provide habitat and food for the Chesapeake’s crabs, fish species and small invertebrates (e.g., sea slugs, sponges).

Underwater grasses help us too—they keep the water clean by absorbing excess nutrients that enter the Chesapeake and reduce erosion by anchoring the sediment on the Bay’s floor and softening waves that break along the shoreline.

But our Bay grasses are in trouble. In 2020, aerial surveys showed a preliminary 62,169 acres across the Chesapeake. This is a 42% decrease from only two years ago, when it was estimated that the Bay supported 108,078 acres. Underwater grasses provide an excellent measure of the Bay’s health, as they respond rapidly to changes in water quality. They require abundant sunlight to grow, so water must be clear enough for it to reach the bottom of the Bay. When pollution or excess sediment clouds the water, the grasses are unable to grow and reproduce.

Climate change is also impacting the Bay’s grass beds. Higher water temperatures and extreme weather—more frequent, stronger storms and droughts—impact their growth and survival. Experts believe these are the causes for the continued decline of widgeon grass—which is referred to as a “boom and bust” species, because it responds rapidly to changes in water quality and extreme weather. The largest decline of grasses over one total area of the Bay in 2020 occurred in the moderately salty waters near Tangier Sound, the mouth of the Choptank River and in the Little Choptank River. Widgeon grass is highly prevalent in these areas and it is believed that an estimated 5,684 acres of grasses disappeared.

The news isn’t all bad. While there was a large decline of grasses between 2018 and 2019, it is estimated that there was only a 7% decline between 2019 and 2020. Chris Patrick, Head of the Chesapeake Bay SAV Monitoring and Restoration Program at the Virginia Institute of Marine Science notes that, “while the 7% decline is disappointing, the silver lining is that the 2020 survey shows that underwater grasses are stabilizing following the losses experienced in the middle Bay in 2019.”

The abundance of grasses in areas of the Bay with either fresh or very salty waters actually increased in 2020, from 17,618 to 18.478 acres, and 11,975 to 13,228 acres, respectively. Grasses in the middle Bay—in slightly and moderately salty waters—continued to decline for a second straight year, falling from 9,029 to 8,086 acres, and 28,061 to 22,377 acres, respectively.

So, how can you help restore the grasses at home? There are lots of different ways!

  • If you live on a tidal tributary of the Bay, or the Chesapeake itself, do not rip out or mow your grasses.
  • If you are a boater, make sure to slow down and trim your motor when you are navigating through a grass bed.
  • Help experts collect data on underwater grasses by becoming a Chesapeake Bay SAV Watcher. This community science-based program asks volunteers to document everything from the types of underwater grass species they see to the presence of shoreline erosion.
  • Do your part to help minimize pollution that may enter the Bay. Recycle, use Bay-friendly pesticides and fertilizers, plant trees to reduce erosion and make sure your home’s downspouts drain onto grass or gravel to lessen stormwater runoff. For more ways to help, check out our How-To’s and Tips.

Under the Chesapeake Bay Watershed Agreement, the Chesapeake Bay Program is working to restore and sustain 185,000 acres of the Bay’s grass beds. Progress toward this goal is measured by meeting a target of 130,000 acres by 2025. Visit ChesapeakeProgress for the most up-to-date information on how we are doing in meeting this important target.



Katherine Bradley

I live off of the Elk River on Herring Creek which is the upper bay and we have gone from very thick beds of sea grass from early July to Fall to essentially nothing this year. Quite a dramatic drop.


I spend 60+ hours a week on the water of the lower, middle bay and rivers. I recall a bay report earlier in the spring suggesting a 40% rise in aquatic vegetation. From my own observation and all accounts from fellow tradesman grasses have been more prevalent than decades previous this year following a trend upward over the last few years. I am curious now how this article and relevant studies appear to arrive at such a contrasting conclusion.

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