YORK COUNTY, Pa. (WHTM) — An aerial blackfly suppression operation has been planned for Wednesday, May 31 for portions of central Pennsylvania.

According to the York County Office of Emergency Management, the operation will be along the main stem of the Susquehanna River. The spraying will begin in Northumberland County and will work its way south toward York County.

The black fly suppression operation will also occur in the following counties:

  • Cumberland
  • Dauphin
  • Juniata
  • Lancaster
  • Mifflin
  • Northumberland
  • Perry
  • Snyder
  • York

The helicopter will be a Bell 205 with the tail number N638HA and is painted blue with silver stripes.

The spray is called Vectobac SC, which is a bacterial larvicide and not a chemical. The substance is a thick brown liquid resembling chocolate milk and is the only product that is used for black fly suppression along the river and other Pennsylvania waterways, which is according to the office of emergency management.

For more information about Vectobac SC, you can view its safety data sheet by clicking here.