How Are the Chesapeake Bay’s Underwater Grasses Doing?

An annual pulse-check of one of the Bay’s most important habitats found a mixed bag. Here’s your guide to understanding the results.

The annual Bay-wide survey of underwater grasses is out, giving insight into one of the most important habitats for the Chesapeake’s fish, crabs, water birds, and other wildlife. Because they depend on clear water, Bay grasses are also a well-known indicator of pollution, earning them a title as the Bay’s “canary in the coal mine.” 

Right now, the canaries are singing mixed messages. Overall, underwater grasses covered an estimated 82,779 acres in 2024, when the latest survey was completed. That’s 1 percent less than they covered the previous year. 

The small drop, however, masks a more complicated story. In parts of the Bay, grasses are thriving—the lower Bay in Virginia saw its largest extent of grasses since the survey began in 1984. But in other areas, notably the mid-Eastern Shore of Maryland, grasses declined enough to offset the gains overall. This boom-and-bust pattern has been common in recent years; usually grasses are doing well somewhere in the Bay, but rarely are they all doing well at the same time. 

A variety of factors are at play. At the end of the day, though, one signal is pretty clear: improving water quality matters. 

A quick primer on the Bay’s underwater grasses

There are over 20 species of underwater grasses found in the Chesapeake Bay. Together they sustain much of its life, providing food and shelter for everything from young blue crabs to overwintering canvasback ducks. They also clarify the surrounding water and can help reduce the effects of climate change. 

Salinity—or how salty the water is—largely determines where different species can grow. In general, the greatest number of species grow in the freshwater reaches of the upper Bay and its tidal rivers, while only two species dominate the saltier waters near the mouth of the Bay. 

These differences are important to understand the grasses’ uneven recovery. 

Where are underwater grasses doing well? 

In 2024, grasses growing in the Bay’s saltiest waters, and grasses growing in freshwater areas did the best. 

• Lower Bay, from the mouth to Virginia-Maryland border: One of the brightest spots was this region, known as the Bay’s “polyhaline”—or very salty—zone. It saw the largest coverage of grass beds since the survey began in 1984. The 24,800 acres recorded in 2024 are approximately 74 percent of the restoration target for this zone. The survey noted that some of the largest gains were in Mobjack Bay, Poquoson Flats, and nearby Western Shore areas.
  

  It’s especially good news because eelgrass, the historically dominant species in this region, is vulnerable to heat and suffered diebacks in 2005 and 2010. Researchers say that improving water quality is a key factor in its resurgence, allowing the grass to grow in deeper, cooler water. 

• Freshwater areas of the upper Bay and tidal rivers: Large meadows of underwater grasses near the mouth of the Susquehanna River, in the upper Chesapeake Bay, have recovered pretty dramatically over the past two decades. Grasses growing in this “tidal fresh” zone, which also includes the freshwater reaches of tidal rivers, reached 20,218 acres in 2024—98 percent of the area’s restoration goal. 

Where are underwater grasses doing poorly?  

Much of the loss in grasses in 2024 was concentrated in areas of the Bay with moderately salty water, known as the “mesohaline” zone. This zone covers the most area in the Bay and has the largest restoration goal. Just a year after seeing promising growth, grass acreage declined to 33,031 acres, just 27 percent of the goal. 

• Mid-Eastern Shore of Maryland and Tangier Sound: The biggest declines happened in the Choptank and Little Choptank Rivers, on Maryland’s Eastern Shore, and around Tangier Sound in Virginia, according to the survey. 

What is the outlook for underwater grasses? 

It’s important to keep these results in context. On one hand, grasses are still far short of restoration targets, which call for 130,000 acres Bay-wide by 2025 and 185,000 acres for full restoration. The closest we’ve been to that number was just over 108,000 acres in 2018. But record river flows washed in more pollution and contributed to a massive die-off in grasses the following year, and they’ve been slowly recovering ever since. 

That being said, grasses growing in the Bay in 2024 covered more than double the area they did in 1984. The long-term trend during that time has been toward more grasses, not less, and that’s a good thing. Researchers also point to areas like the Susquehanna Flats as examples of how quickly grasses can recover when pollution declines and water quality improves. That appears to be happening again in the lower Bay, though the region’s dependence on just two primary species—eelgrass and widgeon grass—makes it vulnerable to big swings if one doesn’t do well in a given year.  

Climate change presents even more challenges and unknowns. A hotter future will likely be problematic for species like eelgrass, though it’s unclear if it might adapt or if other species could take its place (a shift to widgeon grass is already occurring in parts of the lower Bay). More intense rainfall or drought could also cause swings in the Bay’s salt content and the amount of pollution that washes in from farm fields, lawns, and roads. Depending on the conditions they like, different grasses—and different areas—could fare better than others. 

What can we do to help underwater grasses? 

Like all plants, underwater grasses require light to grow. Sediment and algal blooms, caused by pollution washed from the land, can block the sun they need. Reducing pollution and improving water clarity is therefore critical to create the conditions where grasses can thrive. 

The Chesapeake Bay Watershed Agreement guides much of this work. The six Chesapeake Bay watershed states, the District of Columbia, and federal partners who are party to the agreement are currently revising the agreement by the end of this year. A draft is open for public feedback through September 1. CBF is encouraging people to urge leaders to adopt a stronger Bay Agreement that affirms commitments to reach the pollution reductions required by the Clean Water Act, as well as goals to restore underwater grasses and other habitats.