US Army Corps of Engineers
Baltimore District Website

The U.S. Army Corps of Engineers, Baltimore District, is treating hydrilla on Raystown Lake as part of efforts to manage the invasive species and its effects on native ecology. The treatment will take place on July 15, 2020, in just under 83 acres, which represents approximately 1 percent of Raystown Lake. It will focus on a handful of coves where hydrilla is a growing concern.

What is hydrilla?

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)

Why is hydrilla management work important?

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.

How will hydrilla be treated?

The U.S. Army Corps of Engineers will be using endothall, a contact herbicide, to treat hydrilla at Raystown Lake.  Endothall has been safely used at similar sites across the country for years.  

  • Endothall has not been found to be toxic to waterfowl and wildlife at the concentration being applied (3 ppm and under for endothall).
  • It has also been found that this concentration is not toxic to dogs, cats, or livestock incidentally exposed to the herbicide.
  • Native plants are not adversely affected by the treatment because they are largely seed producers, and seeds are not affected by the endothall treatment. 
  • Studies have also been done to test endothall's effect on largemouth bass reproduction, and results show no effect.  If anything, the treatment of the hydrilla should benefit fishing by combatting the hydrilla’s negative impacts on fish populations.

The treatment is expected to take only one morning to complete and the effects on the hydrilla should be noticeable within a few weeks. Follow-up surveys will be conducted in fall 2020 to assess the condition of the hydrilla.

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

 

Will the hydrilla treatment impact recreation and fishing at Raystown Lake?

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 treatment scheduled for the early morning hours of July 15th. Other than the few morning hours when contractors are on-site carrying out the treatment, there will be no restricted access associated with this work.

The work will be done on just under 83 acres of Raystown Lake, which represents approximately 1 percent of the lake. That approximately 1 percent of the lake will primarily be in a handful of coves where hydrilla is present and not in areas of heavy boating traffic.

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 several 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.

General information

The Corps of Engineers is authorized to treat Hydrilla (hydrilla verticillata) under Section 104 of the River and Harbor Act of 1958, through the Aquatic Plant Control Research Program. Funding for the project is available through the Corps of Engineers Aquatic Plant Control Research Program.

The scheduled treatment on July 15, 2020, will mark the first time hydrilla has been treated at Raystown Lake. Raystown Lake has had hydrilla for years, but 2020 is the first year funding was made available to carry out the treatment at the site.