PUBLIC NOTICE: Maryland Agencies to Treat Potomac River for Black Fly Control on June 24

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ANNAPOLIS, MD (June 22, 2026) ~ Annapolis, MD - The Maryland Department of Agriculture, in collaboration with the Department of Natural Resources, has announced plans to control black fly populations in the Potomac River near Harpers Ferry, West Virginia. The treatment is set to take place on Wednesday, June 24, 2026 between 8:00 a.m. and 10:00 a.m. ET.

To carry out the treatment, a blue-and-gray Bell 206 Long Ranger helicopter with tail number 651HA will be used to apply a Bacillus thuringiensis israelensis (Bti)-based larvicide throughout the targeted area. Bti is a naturally-occurring bacterial insecticide that poses no harm to humans or other organisms outside of its targeted insect groups such as midges, black flies, and mosquito larvae.

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While the treatment may cause temporary discoloration of the water, it is completely harmless and will dissipate on its own. There will be no impact on drinking water supplies or aquatic life such as fish and crabs.

The Black Fly Program was established in 2016 after receiving numerous complaints from residents in Washington County. For more information about the program and Bti, interested individuals can visit the Maryland Department of Agriculture's Black Fly Program website.

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