What is Hydrilla?

Hydrilla is a non-native invasive aquatic plant that grows in dense branching colonies which can grow in water up to 20 feet deep and form thick mats across the water’s surface.

Hydrilla is well suited to live in a variety of freshwater habitats including, lakes, ditches, rivers and marshes. The plant is tolerant of nutrient levels and its ability to grow in low-light conditions means it can grow at deeper depths and begin photosynthesizing earlier in the day than many other aquatic plants. Hydrilla can reproduce in four different ways including fragmentation, tubers, turions, and seed. With these adaptations in addition to the large, thick mats and rapid growth rate, Hydrilla is able to out compete most native vegetation that it encounters.

Hydrilla is listed as a Federal Noxious Weed, and it is therefore illegal to import or sell the plant in the United States as millions of dollars are spent annually in the U.S. to control the growth and spread of the plant in our nation’s waterways.

Photo credit: Ryan Argo, ORSANCO.

Why is Hydrilla problematic in our lakes?

Aside from the adaptations that allow Hydrilla to out-compete native aquatic vegetation, creating a monoculture that decreases biodiversity, the rapid growth rate and thick mats can increase water pH and temperature and cause wide fluctuations in dissolved oxygen. The growth rate and density of Hydrilla can also have significant impacts on water intake structures by clogging pipes and can decrease recreational opportunities as entire coves can become inaccessible for boating and swimming.

Photo credit: Ryan Argo, ORSANCO. Hydrilla infestation in the Ohio River.

How to prevent the spread of Hydrilla

• Remove all plant fragments from your boat, propeller, and boat trailer. The transportation of plant material on boats, trailers, and in livewells is the main introduction route to new waterways. You should always thoroughly clean your boat before and after visiting different lakes.
• Rinse any mud and/or debris from equipment and wading gear and drain any water from boats before leaving a launch area.
• Do NOT release aquarium or water garden plants into the wild, rather seal them in a plastic bag and dispose in the trash.
• Consider using native plants from your state in aquariums and water gardens.
• If you detect this plant in a waterway contact the appropriate state authority. Links for each of the states within the Louisville District’s area of responsibility are included on this page.

Photo credit: Ryan Argo, ORSANCO. Hydrilla infestation in the Ohio River.

What is the Corps doing about Hydrilla?

The U.S. Army Corps of Engineers- Louisville District is working with Kentucky Department of Fish and Wildlife Resources and the U.S. Forest Service to craft a treatment plan for lakes affected by Hydrilla in Kentucky.