Some of these sites refer to the lake in question as being currently named Lake Webster, but this site says it's locally known as Lake Manchaug: http://www.mchs.net/MCHSLIB/HTML/didknow4.html
And finally, an answer to what I thought would be another Eternal Question, "What is the proper term for a word like Chargoggagoggmanchauggagoggchaubunagungamaugg (besides 'long')?" It's called a hippopotomonstrosesquipedalian, according to this site: http://jewel.morgan.edu/~salimian/humor/humor_203.html