Ask Claire Snyder about the discovery of hydrilla in DuPage County, and she doesn’t hold back. “I am kind of calling it public aquatic plant enemy No. 1,” Snyder says.

The airboat is part of an ongoing study to track the spread of Hydrilla, a water plant that has been wreaking havoc on the river for years. Keith Hannon, from the New England District of the U.S ...