Chemical Management of Hydrilla for Drinking Water Utilities

Last Modified: Nov 08, 2018


  • Ben Wright, Meredith Taylor, Mike Usai, Tina Nelson

Hydrilla verticillata (hydrilla) is a federally listed aquatic invasive species that has the potential to cause significant economic and environmental impacts once established. Introduced decades ago in Florida and the Mid-Atlantic states, hydrilla has continued to spread through much of the US. Hydrilla is a high priority risk for reservoir systems as it can impact water quality, aquatic habitat, and recreational uses. The species forms dense mats of vegetation, outcompeting native species, reducing dissolved oxygen, and raising pH. Decay of plant litter can increase natural organic matter in reservoirs, which is a precursor to disinfection byproduct formation. Control of hydrilla is expensive; Florida and California each spend millions of dollars annually on hydrilla control. However, without management, Hydrilla can take over and can make lakes nearly unusable. As with other aquatic invasive species, once a population is established, management alternatives consist of chemical, biological, physical, or mechanical/manual methods. However, hydrilla’s ability to reproduce from plant fragments, turions and tubers, has made chemical management with herbicides one of the most common methods of control.

Hydrilla, therefore, poses a unique problem in sources of drinking water. The foremost responsibility of drinking water managers is to maintain public health. Utilities expend significant effort to protect the quality of their sources of drinking water and prevent contamination. For a utility or water manager to decide to add chemicals to a source of drinking water, they must be assured that those chemicals are not going to cause harm to the general public. As hydrilla continues to spread, it will inevitably affect more sources of drinking water. Therefore, the Water Research Foundation, in partnership with the New York City Department of Environmental Protection (DEP), funded this project to:

  • Assess the state of knowledge of herbicide application for the management of hydrilla in drinking water reservoirs and its impacts on treatability, water quality, and human and environmental health;
  • Review lessons-learned from prior hydrilla management efforts;
  • Provide recommendations for mitigation of impacts associated with hydrilla management; and
  • Develop communications resources for public outreach.
  • This presentation will provide an overview of the project findings, which will help the audience obtain a better understanding of the potential risks from hydrilla and communicate those risks to stakeholders, so utilities can respond quickly and effectively to hydrilla infestations.

    For more information, please contact the author at

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