After 30 years of having the name and the meaning (albeit, not the spelling) memorized, I finally know where it is!

Lake Chargoggagoggmanchaugagoggchaubunagungamaugg, a name derived from a Nipmuc Native American tribe transates "fishing place at the boundary" but townspeople prefer the innaccurate translation: "You fish on your side, we'll fish on our side, and nobody will fish in the middle." It is often regarded as the longest place name in the United States. A shorter name for this body of water is Lake Chaubunagungamaug, or simply Webster Lake.