In his journal Champlain wrote of local Indians describing a fish with "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."
Though often claimed as an eyewitness report of "America's Loch Ness Monster," his description is clearly that of a sturgeon-like gar fish.
Another reason that the sturgeon seemed monstrous was that it's an unusually large fish.
The fish most people (and certainly most urban dwellers) encounter are relatively small - goldfish perhaps, or aquarium fish. Sport fishermen, butchers and marine biologists are far more likely to recognize large fish such as tuna, sturgeon and gar, for example, which often grow to surprising sizes.
Even seeing large fish on television, in aquariums or in photographs does not necessarily prepare city-dwelling beachgoers for real-life encounters with a beached, smelly giant.