Lake Champlain is the sixth largest freshwater lake in the United States, and acts a natural border between Vermont and New York. The only way to cross is a bridge near Chazy, New York, or to take a ferry from Plattsburgh, New York, or Port Kent.
The lake was first explored by Frenchman Samuel D. Champlain in the 1600s, and he was the first European to have a sighting of the (locally) legendary monster, Champ, (although the monster is known as Champy to locals.)
Lake Champlain has been host to quite a few (not so) famous battles including the Battle of Valcour, and the Battle of Plattsburgh, two pivotal battles that halted British expeditions into New England during the Revolutionary War, and the War of 1812 respectively.
One final piece of useless lake trivia: Lake Champlain was actually named the sixth Great Lake for about a week back in the late nineties (96' I think). A sneaky New York senator slipped it through legislation even though it was only 1/17 the volume of the next largest Great Lake. It caused a lot of local stir because of the fifteen minutes of fame it brought the region, but the senate finally realized it had been had, and quickly repealed the unpopular decision.