Aerial Spraying for Black Flies | Delaware and Lehigh Rivers

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The Pennsylvania Department of Environmental Protection (DEP) will be conducting an aerial black fly suppression operation on the Lehigh River beginning at 12:00 PM on Tuesday June, 4, 2024. This operation will proceed to the confluence of the Delaware River in Easton. Any portion not treated on Tuesday, June 4, will be treated on Wednesday, June 5, beginning at approximately 8:00 AM. In addition, on Wednesday, June 5, the Delaware River will be treated from the Portland area in Northampton County to Trenton, NJ/Yardley, PA, in Bucks County.

The helicopter conducting the treatment will be a green and white Bell 206L3 with tail number N641HA. The aircraft is operated by Helicopter Applicators of Gettysburg, PA. DEP personnel will be on-site at all landing zones, managing the operation.

Vectobac 12AS is B.t.i. product manufactured by Valent Biosciences. The B.t.i. material is a naturally occurring bacteria (Bacillus thuringiensis israelensis) that kills the immature (larval) form of the black fly when they feed on it in the waterways. It is a bacterial larvicide, not a chemical, and is the only product used in Pennsylvania’s waterways for black fly suppression. B.t.i. is not toxic to fish or other aquatic macroinvertebrates found in the treated waterways, degrading quickly in the environment.

Black flies, also known as biting gnats, are considered a pest that can inundate people seeking outdoor recreation in the warmer months, especially around rivers and streams.

For more information on the program, please visit the Black Fly Program website: Black Fly (



Information provided to TVL by:
County of Northampton
669 Washington Street
Easton, PA 18042