ANNAPOLIS, MD (May 11, 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 Tuesday, May 12, 2026 between 9:00 a.m. and 10:00 a.m. ET.

To carry out the treatment, a green-and-gold Bell 206 Long Ranger helicopter with tail number N637HA 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. Drinking water supplies, fish, crabs, and other aquatic organisms will not be affected by the treatment.

The Black Fly Program was established in 2016 after concerns were raised by residents in Washington County. More information about the program and Bti can be found on the Maryland Department of Agriculture's Black Fly Program website.

This targeted treatment aims to reduce black fly populations in the area and alleviate any potential nuisance for residents and visitors alike. The Maryland Department of Agriculture assures that all necessary precautions have been taken to ensure the safety and well-being of both humans and other aquatic life during this process.

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