Plesiosaurs

Plesiosaurs are water-dwellers in the lakes of the valley of Eodon, that grow to impressive sizes. The adventurer is perfectly safe from them, as long as he/she stays away from water or swamp. However, should someone be stupid enough to enter the territory of the Plesiosaur, it will see this as an invitation from a quick, fresh snack.

Safe means have to be found first, to cross these waters.

Lore
''This is a water-dwelling dinosaur dating to the early Jurassic (some 200 million years ago). Growing to twenty to twenty-five feet in the valley, the plesiosaur is a dangerous and aggressive animal. Certain outer-world descendants of the species grew to more than forty feet in length, and may well be represented in the deeper waters of the valley. The still waters (such as the swamps) are sufficiently rife with them that it is unsafe to cross except on a raft or perhaps on the back of an accommodating apatosaurus or archelon.''

-from "Ultimate Adventure Magazine", Savage Empire