Invasive Water Lettuce Harms Bay Grasses And May Impede Boating

No Gravatar

Dept. of Natural Resources Urges Proper Disposal of Water Garden & Aquarium Plants

Invasive Water Lettuce Harms Bay Grasses And May Impede Boating ANNAPOLIS, MD —  The Maryland Department of Natural Resources (DNR) reminds water gardeners and aquarium owners to properly dispose of aquatic plants to prevent spread of invasive species like water lettuce that harm bay grasses and may impede boating. DNR biologists first identified invasive water lettuce (Pistia stratiotes) in Maryland last summer during a routine survey of Mattawoman Creek, a large Potomac River tributary in Charles County.

“Water lettuce has the potential to severely impact our waterways,” said Mark Lewandowski, DNR biologist. “This aquatic invader blocks sunlight from reaching critical bay grasses and decreases oxygen exchange at the water’s surface.”

A native of South America, water lettuce is an aquatic weed that floats on the surface of slow-moving rivers, lakes and ponds. Unmistakable in appearance with light green leaves grouped in rosette like an open head of lettuce, the commonly used household aquatic plant floats on the surface of the water alone or in dense mats. Water lettuce produces seeds and spreads rapidly; growing into thick mats of vegetation that block sunlight from reaching underwater grasses and using dissolved oxygen in the water that fish need to survive. Once established, water lettuce becomes impenetrable to boats, swimmers and waterfowl.

DNR hopes to eliminate this invader and advises boaters, swimmers and residents to keep a look out for its presence and take precautions to avoid its spread to other streams and rivers. New introductions of the plant result from improper disposal of domestic pond plants and water, or when winter rains overflow man-made ponds into local bodies of water. Water lettuce may also be introduced by hitchhiking on boat trailers or other gear.

Invasive Water Lettuce Harms Bay Grasses And May Impede Boating Residents surrounding the Potomac River are encouraged to help DNR eliminate invasive water lettuce. Water lettuce can be raked or seined to remove it from the water’s surface and then either spread out on the ground away from water to dry out and die or bagged up with compost.

“Water lettuce does not root to the river or stream bed, so the simplest way to remove it is to pull it from the surface with a net or your hands. If you see a floating mass of them, try to remove them and place them on land away from water or in a trash bag,” advises Lewandowski.

Warm summer weather is the ideal time for water lettuce to flourish. Individuals who spot water lettuce in Maryland’s waterways are encouraged to remove it and also report what they see to DNR by calling 410-260-8634 or emailing mlewandowski [at] dnr [dot] state [dot] md [dot] us.

For additional information on water lettuce and other invasive species, visit