Underwater Grasses

By providing food and habitat for wildlife, reducing shoreline erosion and improving water clarity, underwater grasses play an important role in the Bay ecosystem.

Bar graph illustrating the number of acres of underwater grasses in the Chesapeake Bay from 2000 to 2019.

Underwater Grasses

In 2020, an estimated 62,169 acres of underwater grasses were mapped in the Chesapeake Bay and its tidal tributaries. This is a 60% increase from the 38,958 acres mapped during the first survey in 1984, but a 20% decrease from the current 10-year average of 78,168 acres and a 7% decrease from 2019 when 66,684 acres of underwater grasses were mapped.

62,169

Acres of underwater grasses in the Chesapeake Bay

Experts attribute the losses largely to a decline in widgeon grass, a species whose abundance can rise and fall from year to year in response to changes in water quality. For example, in 2018, widgeon grass increased in various parts of the Bay before subsequently declining in 2019. This mirrors a similar rapid increase in 2001 and 2002 that was followed by about a 50% decline in 2003. Though the precise cause for the fall in widgeon grass is unknown, a contributing factor may have been higher than average freshwater entering the Bay from rivers through 2019, which reduces water clarity and blocks sunlight from reaching the plants.

The 62,169 acres mapped in 2019 marks 34% achievement of the 185,000-acre goal adopted by Chesapeake Bay Program partners in the Chesapeake Bay Watershed Agreement. A continued rise in bay grasses will benefit the entire Bay ecosystem: underwater grasses absorb nutrient pollution, improve water clarity, reduce shoreline erosion, release oxygen into the water, sequester carbon and provide food and shelter to striped bass, blue crabs and other critters. 

To learn more about our progress toward achieving and sustaining 185,000 acres of underwater grasses Bay-wide, visit www.ChesapeakeProgress.com.