Endothall is a selective contact herbicide that is being applied to the Cayuga Inlet in the continued effort to eradicate Hydrilla. Endothall kills the growing green vegetation that it contacts in the water by disrupting photosynthesis. Hydrilla is much more sensitive to the effects of endothall than most native plants. The chemical degrades naturally by bacterial action in the water and has a half-life ranging from 5 to 8 days. The commerical name is Aquathol K (active ingredient dipotassium endothall 40.3%). We obtain Aquathol K from United Phosphorous, a company based in Pennsylvania. Read more about endothall and view the Aquathol K label providing information about its legal use.

Where and How is Endothall Applied?

During the 2011 treatment season through the 2015 treatment season, endothall was applied in the Cayuga Inlet, the Flood Control Channel, Treman Marina and the lower reaches of Cascadilla and Six Mile Creeks. Endothall has been applied to Fall Creek starting from the 2013 treatment season to the 2016 treatment season. Licensed herbicide applicators apply the herbicide using a boat where possible and backpack sprayers in less accessible areas. The application equipment uses hoses and nozzles to inject the herbicide application below the surface of the water for the entire treatment.

During the application process a cloud or mist may be seen behind the air boat. It is known as "prop wash," which refers to the column of air and water emitted rearward from an air boat by the propeller. It is not related to the herbicide chemicals or application in any way.

What are the Health Impacts?

Drinking water quality is closely monitored.

  • Endothall is applied to Cayuga Inlet at a concentration rate of 2-4 ppm (parts per million). Water may not be used as drinking water until the concentration is below the New York State Maximum Contaminant Level (MCL) of 0.05 ppm or 50 ppb (parts per billion). Endothall is expected to be below the MCL in the application areas within 10-14 days due to dispersion, dilution and degradation.
  • The Bolton Point Water Treatment Plant is located 3 miles away from the herbicide application area. Water samples are collected at the water supply intake until at least 14 days following the endothall application. Results will be posted at StopHydrilla.org.
  • While the MCL is not expected to be exceeded at Bolton Point, it will be exceeded at other locations in the inlet and possibly in Cayuga Lake. Water taken directly from the lake should never be used for drinking.
  • Animal consumption of the treated water is prohibited for 14 days.

Swimming is prohibited in the treatment area until one day after the endothall application.

Endothall is poorly absorbed through the skin. Minor skin and eye irritations have been reported in people who are regularly exposed to concentrated levels of endothall in the course of their work, but no effects have been observed as a result of occasional exposure. Swimming outside of the treatment area is not affected.

Fishing is unrestricted.

  • There are no restrictions on catching and eating fish.
  • Endothall does not accumulate in animal tissue. Fish and livestock that consume water treated with endothall rapidly excrete the chemical.

Use of lake water for irrigation restricted.

Because endothall is an herbicide, do not use lake water for irrigation or spraying of grass or agricultural crops until at least 7 days after the application.

Water use restrictions were supplied along the water with the yellow herbicide warning signs. 

Last updated July 26, 2019