The Conways' boat trip and the subsequent monster attack are described as happening on a moonlit night, yet all scenes take place in broad daylight.
A man falls out of his boat, and the monster drags him under and eats him. The boat is found later with a lot of bloody water inside.
When Sheriff Steve is chasing the robber, the same 1971 Chevrolet Kammback passes them that was seen parked at the Palomar Cafe.
In most scenes, the monster appears being reddish-gray. But when he attacks the cows, he is solid gray.
The Crater Lake Monster is a plesiosaur, yet it is constantly called a dinosaur. They are completely separate orders of animals, yet even a paleontologist, who should know the difference, makes this mistake repeatedly.
Crater Lake was formed by the cataclysmic eruption of Mount Mazama less than 8,000 years ago. It would be impossible for 65-million-year old plesiosaur eggs, fossilized or otherwise, to be present on the lake floor.
Dan Turner is described as a paleontologist, an expert in fossilized animals, yet he seems to be working as an anthropologist throughout the film .
The lake shown throughout the movie bears no resemblance to the real Crater Lake.
After being attacked by the Plesiosaur,the Sheriff comes back with the local Doctor shows him the imprints of the creature with a flashlight even though it is daylight.
After fleeing from the Plesiosaur,the Sheriff is seen driving with it being dark all around him even though it is daylight moments later.
The Sheriff car and ambulance both have regular private owner California license plates. Usually these would have special "Exempt" plates.
A character says Crater Lake is "four hours from Vegas." It's about 750 miles, and driving takes about 12 hours.
Crater Lake is within a National Park, with no town on its shores.
The boats and cars have California registration numbers/plates. Crater Lake is in Oregon.
The mysterious disappearance (and death) of a sitting U.S. Senator should be a major event, yet none of the characters-including the ranking local lawman-seem to care.
Even though suspending all disbelief that a plesiosaurus egg could miraculously hatch after laying dormant in cold water for millions of years, how on earth can it grow into a 100ft monster in a matter of days? It's received no care or food and it survived totally submerged and then went through it's sneaky destruction trying not to get caught.
Two characters say there's not much business on the water, as a boat travels by in the background.