SCHROON, N.Y. — Nosing into a shallow bay on Schroon Lake, Steve LaMere peered over the side of his pontoon boat. He was on an unusual reconnaissance mission, looking for signs of an aggressive aquatic invader, a stringy herb from Eurasia that once adorned American aquariums but has no business here in the Adirondacks — or anywhere in North America. “I’m a fifth-generation Adirondacker, and I take this stuff personally,” said Mr. LaMere, a certified lake manager and ecologist who is on the front lines of the fight against invasive species. “The Adirondack Park is where I’ve drawn my line...
