Hydrilla is an aquatic plant that has earned the illustrious title “world’s worst invasive aquatic plant”. Listed as a federal noxious weed, hydrilla has made its home in just about every conceivable freshwater habitat including rivers, streams, lakes, ponds, marshes, canals, ditches, and reservoirs.

Hydrilla was first discovered in the United States in the 1960s in Florida. Since then, it has spread to many parts of the U.S.

Hydrilla can grow in a wide variety of water conditions (e.g., high/low nutrients, high/low turbidity, variable pH, up to 7% salinity) and water temperatures.  Unlike most native aquatic plants, hydrilla is capable of growing under extremely low light conditions. Hydrilla is able to begin photosynthesizing much earlier in the morning than native plants, so it is able to capture most of the carbon dioxide in the water (which limits growth of other plants).  Hydrilla grows very rapidly (it can double its biomass every two weeks in summer) and has no natural predators or diseases to limit its population.

Dense infestations of hydrilla can shade or crowd out all other native aquatic plants, alter water chemistry, cause dramatic swings in dissolved oxygen levels, increase water temperatures, and affect the diversity and abundance of fish populations.

(Via the U.S. Fish and Wildlife Service)

Hydrilla is an invasive species that can negatively affect local ecosystems. Dense infestations of hydrilla can shade or crowd out all other native aquatic plants, alter water chemistry, cause dramatic swings in dissolved oxygen levels, increase water temperatures, and affect the diversity and abundance of fish populations. Hydrilla also has negative impacts on recreation, including making it more difficult or even potentially dangerous for both boating and swimming due to the denseness of its growth.

By treating the hydrilla to suppress its growth, the intent is to diminish these negative effects and in turn benefit Raystown Lake’s natural ecology.

The U.S. Army Corps of Engineers uses aquatic herbicides such as endothall or fluridone to treat hydrilla at Raystown Lake.  Both herbicides are high effective on hydrilla and have been safely used at similar sites across the country for years.  Raystown’s 2023 treatment will be using fluridone.

• There are no restrictions on swimming, eating fish from treated water bodies, human drinking water, or pet/livestock drinking water at application rates.
• Fluridone does not appear to have any apparent short-term or long-term effects on fish.
• Studies on birds indicate that fluridone would not pose an acute or chronic risk to birds.
• Plants vary in their susceptibility to fluridone, so some species will not be affected.

The treatment will require three applications over a nine week period from mid-May to mid-July 2023. The treatment will require three days of actual herbicide application. Follow-up surveys will be conducted in fall 2023 to assess the hydrilla within the treated areas.

Unless visitors see the contractors carrying out the treatment, they should not notice any visible changes or impacts in the water beyond the eventual reduction in hydrilla.

The hydrilla treatment should have minimal impact to recreation at Raystown Lake, if any. There will not be any closures of boat launches or swimming restrictions associated with the treatment. Other than the few morning hours when contractors are on-site carrying out the application, there will be no restricted access associated with this work.

The work will be done on 50 acres, which represents approximately 0.6 percent of the Lake. The treatment will focus on a handful of coves where hydrilla is a growing concern.

Regarding fishing, the treatment should have minimal to no impacts on fishing. While coves are popular fishing spots, only a handful of the coves will be treated and there will be numerous coves where no work is taking place. Even the coves where work is taking place will still be available for fishing outside the morning hours when contractors are on site carrying out treatment.