Underwater grasses—also known as submerged aquatic vegetation or SAV—are plants that grow in the shallow waters of the Chesapeake Bay and its streams, creeks and rivers. Underwater grasses are a critical part of the Bay ecosystem: they provide wildlife with food and habitat, add oxygen to the water, absorb nutrient pollution, trap sediment and reduce erosion. Like all plants, underwater grasses need sunlight to grow, which makes improving water clarity an important step in underwater grass restoration.
Also known as submerged aquatic vegetation, or SAV, underwater grasses are plants that grow in the shallow waters of the Chesapeake Bay and its streams, creeks and rivers, and are a critical part of the Bay ecosystem.
Underwater grass beds are critical to the Chesapeake Bay ecosystem. They offer food to small invertebrates and migratory waterfowl; shelter young fish and blue crabs; and keep our waters clear and healthy by absorbing excess nutrients, trapping suspended sediment and slowing shoreline erosion.
These grasses also act as an excellent measure of Chesapeake Bay health. Although underwater grasses are sensitive to pollution, they respond fairly quickly to improvements in water quality. This means their abundance is a good indicator of restoration progress.
You can watch changes in underwater grass abundance over time using this interactive map.
Bay grass beds provide food and shelter to a number of wildlife species, many of which depend on each other for survival.
Underwater grasses also add oxygen to the water during photosynthesis. Underwater critters need oxygen to survive.
Underwater grass beds help keep the Chesapeake Bay clean and healthy by:
Just like plants on land, underwater grasses go through photosynthesis to convert sunlight into food. Sunlight, therefore, is the most important factor determining grass survival. Water must be clear enough for sunlight to pass through it and reach the grasses that grow on the bottom of rivers, streams and the Chesapeake Bay.
Underwater grass growth is hindered by pollutants that cloud the water. These pollutants include excess nutrients—which fuel the growth of dense algae blooms—and suspended particles of sand, silt and sediment.
Healthy underwater grass beds can trap and absorb some of this nutrient and sediment pollution, but too much of it can block sunlight from reaching the plants.
Extreme weather, including high temperatures or excess rainfall, can harm underwater grasses.
Some species, like eelgrass, cannot grow in water that is too warm. In 2005, high temperatures caused large beds of eelgrass in the lower Chesapeake Bay to die. It can take several years for underwater grass beds to recover from these kinds of large-scale losses.
Precipitation—and the water-clouding pollution it pushes into rivers and streams—has a big influence on underwater grass growth.
Modern science allows researchers to target underwater grass restoration to those areas where grasses once grew. But poor water quality, irregular weather and a lack of funding have slowed restoration progress.
Chesapeake Bay Program partners use four initiatives to restore and maintain the health of underwater grasses: improving water clarity, planting underwater grasses, protecting existing grass beds and enhancing underwater grass-related education and outreach.
Improved water clarity is critical to underwater grass restoration because clouded water can block sunlight from reaching aquatic plants. When water is clear, more sunlight can reach the bottom of rivers, streams and the Chesapeake Bay, fueling the growth of new grasses and the expansion of existing grass beds.
Maryland, Virginia and the District of Columbia have outlined water clarity standards for the shallow waters where underwater grasses grow or once could be found. These standards list the amount of sunlight that must be able to pass through the water.
Pollution reduction efforts—including the Bay “pollution diet,” or Total Maximum Daily Load (TMDL)—aim to slow the flow of nutrients and sediment into the Bay and its waterways. Upgrades to wastewater treatment plants and on-farm conservation practices, for example, are expected to improve water clarity.
Although underwater grasses can naturally colonize an area faster than we can spread them through planting, planting underwater grasses can lead to restoration success, enhancing the natural expansion of healthy grass beds.
The Maryland Department of Natural Resources (DNR), for instance, led two large-scale eelgrass restoration projects on the Patuxent and Potomac rivers between 2003 and 2007. Scientists found that distributing seeds collected from healthy grass beds elsewhere could accelerate the natural expansion of weaker eelgrass beds. Scientists need sustained funding and adequate plant and seed supplies to continue this kind of work.
Underwater grass beds can be damaged by a number of things, including human activities, invasive species and climate change.
A number of organizations are teaching citizens about the importance of underwater grasses:
As part of the Chesapeake Bay Watershed Agreement, Chesapeake Bay Program partners have committed to the goal of achieving and sustaining 185,000 acres of underwater grasses in the Bay, with a target of 90,000 acres by 2017 and 130,000 acres by 2025.
For Chesapeake Bay restoration to be a success, we all must do our part. Our everyday actions can have a big impact on the Bay. By making simple changes in our lives, each one of us can take part in restoring the Bay and its rivers for future generations to enjoy.
To support underwater grasses in the Bay watershed, boaters can follow posted speed limits and no-wake laws to avoid harming grass beds. Boaters can also steer clear of any grasses growing in shallow waters.
The 2015 acreage exceeds the 2017 restoration target two years early
Widgeongrass grows where vegetation was not mapped before
Scientists attribute the boost in bay grasses to the expansion of widgeon grass in saltier waters.
Scientists link a Clean Water Act permit program to healthier rivers and streams.
New research suggests higher-quality grass habitat could boost Chesapeake Bay blue crab populations.
In 2015, there were an estimated 91,621 acres of underwater grasses in the Chesapeake Bay. This surpasses the Chesapeake Bay Program’s 2017 restoration target two years ahead of schedule and marks a 49 percent achievement of the partnership’s 185,000-acre goal.
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.
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.
Publication date: March 28, 2012 | Type of document: Backgrounder | Download: Electronic Version
In 2011, 57,956 acres of underwater bay grasses in Chesapeake Bay and its tributaries were mapped via aerial survey.
However, while the entire Bay was flown, some portions of the Bay were not mapped since SAV signatures were
masked by…
Publication date: April 21, 2011 | Type of document: Backgrounder | Download: Electronic Version
In 2010, 79,675 acres of underwater bay grasses were mapped in Chesapeake Bay and its tributaries.
Publication date: April 27, 2010 | Type of document: Backgrounder | Download: Electronic Version
In 2009, 85,899 acres of underwater bay grasses were mapped in Chesapeake Bay and its tributaries. This is a 12 percent increase from 2008, when 76,860 acres were mapped.
Publication date: April 29, 2009 | Type of document: Backgrounder | Download: Electronic Version
Backgrounder: Underwater Bay Grasses in the Chesapeake Bay and Rivers in 2008
Publication date: December 01, 2003 | Type of document: Policy Memorandum | Download: Electronic Version
This document presents a strategy to accelerate the protection and restoration of submerged aquatic vegetation, or SAV, in the Chesapeake Bay and its tidal tributaries.
Publication date: September 22, 2003 | Type of document: Backgrounder | Download: Electronic Version
Bay grasses are a unique yardstick for measuring the progress of Chesapeake Bay restoration efforts because they are not under harvest pressure and their health is closely linked to water quality. In recent years both the health and…
Publication date: September 22, 2003 | Type of document: Backgrounder | Download: Electronic Version
In 2002, SAV coverage reached a record 89,658 acres - more than twice the level first recorded in 1978. While this increase is impressive, a great deal more needs to be done to reach the Bay Program’s new 185,000-acre baywide restoration…
Publication date: May 01, 2001 | Type of document: Backgrounder | Download: Electronic Version
The distribution of submerged aquatic vegetation (SAV) in Chesapeake Bay, its tributaries, and the coastal bays of the Delmarva Peninsula, was mapped from 2,033 black and white aerial photographs. These were taken between May and October…
Publication date: May 01, 2000 | Type of document: Backgrounder | Download: Electronic Version
Number of Hectares of SAV in 1999 and 2000 and Percent Change for Chesapeake Bay Segments and Zones