Naveed on his blog Naveed's Realm has an interesting item about the legend of the monster in Devil's Lake in Lincoln City, Oregon.
The short story as for as the Oregon one goes is that the Siletz Indian tribe centuries ago used to really like of the area of Devil's Lake. Then one night when a group of warriors was dispatched across the lake, massive tentacles burst forth from the waters destroying the canoes. The warriors where then flung around, beaten against the water and debris, and died from drowning or injury. From then on the lake was called Devil's Lake.
Was the "monster" a squid, or is the story only a myth to explain the dangers of the area?