Thanks GC, I can't copy and paste hyper links for some reason. Anyway,the following is from Wikipedia and the Lake Champlain Heritage Foundation.
The indigenous people that have long lived and hunted near Lake Champlain, the Abenaki and the Iroquois, have their own legends about a large creature inhabiting the lake, which looked like a large, horned serpent or giant snake. The Abenaki term for this creature is Gitaskog. Early in the 18th century, Abenakis warned French explorers about disturbing the waters of the lake, so as not to disturb the serpent. Samuel de Champlain, whom the lake is named after, is often erroneously credited with being the first European to sight Champ, but readings of his accounts show that he saw something near the St. Lawrence River. Nevertheless, his account of his sighting is of interest to anyone with an interest in lake monsters!
Champlain described what he saw like this: ". . . [T]here is also a great abundance of many species of fish. Amongst others there is one called by the natives Chaousarou, which is of various lengths; but the largest of them, as these tribes have told me, are from eight to ten feet long. I have seen some five feet long, which were as big as my thigh, and had a head as large as my two fists, with a snout two feet and a half long, and a double row of very sharp, dangerous teeth. Its body has a good deal the shape of the pike; but it is protected by scales of a silvery gray color and so strong that a dagger could not pierce them."
Historians think Champ is probably a garfish, a class that includes lake sturgeon, which still live in Lake Champlain today. Champlain's description of the creature sounds very much like a garfish, albeit much larger than usual.
https://www.lakechamplainregion.com/heritage/champ
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In American folklore, Champ is the name of a lake monster said to live in Lake Champlain, a 125-mile (201 km)-long body of fresh water shared by New York and Vermont, with a portion extending into Quebec, Canada.
https://en.wikipedia.org/wiki/Champ_(folklore)