The Department of Environmental Protection has begun aerial spraying on more than 1,600 stream miles in 36 Pennsylvania counties to control black flies, also referred to as gnats.

The Schuylkill River in Schuylkill County, as well as the Lehigh River in Lehigh and Northampton counties and the Delaware River in Northampton County, will be included in this round of spraying.The first aerial spraying took place on April 27 along the Schuylkill River. Other waterways will be treated as stream flows and weather conditions allow.DEP uses Bti, a naturally occurring bacterium, to treat the larval stage of four specific human pest black fly species. This bacterium degrades quickly in the environment and does not harm the aquatic ecosystem, birds or other insects.DEP notifies county and local emergency management officials before any spraying activity.Helicopters seen flying over waterways and ground crews using backpack sprayers off bridges are conducting control operations on behalf of DEP's black fly program. Anyone concerned at the sight of a helicopter or ground personnel is encouraged to call their county emergency management office to verify that a black fly treatment is taking place in their area on that day.