A few years ago a shark researcher offered a new theory about what might be behind some of the world’s famous lake monsters.

Bruce Wright, a senior scientist at the Aleutian Pribilof Island Association, wrote an article for the Alaska Dispatch newspaper that proposed an interesting idea: “For years, legendary tales from Scotland and Western Alaska described large animals or monsters thought to live in Loch Ness and Lake Iliamna. But evidence has been mounting that the Loch Ness and Lake Iliamna monsters may, in fact, be sleeper sharks.”

Wright suggests that the sharks, which can reach 20 feet long and weigh more than 4 tons, might migrate through rivers and into lakes and be mistaken for monsters. The Lake Iliamna monster (known as Illie) is said to resemble a whale or a seal and be between 10 and 20 feet long. There have been fewer than a half dozen sightings of Illie since it was first seen in 1942.

The best known American lake monster is not said to be in Alaska but instead in Lake Champlain, which forms the border between Vermont and New York. “Champ,” as the creature is called, has allegedly been seen by hundreds of witnesses and is anywhere between 10 and 187 feet long, has one or more humps, and is gray, black, dark green or other colors.

The best evidence for Champ—in fact, for any lake monster—was a 1977 photo taken by a woman named Sandra Mansi showing what appeared to be a dark head and hump in the lake. Later investigation by myself and Joe Nickell revealed that the object was a floating log that looked serpentine from a certain angle.

While Wright’s hypothesis is interesting, there are many problems with his theory, including the fact that both Ness and Iliamna are freshwater lakes, while Pacific sleeper sharks, as their name suggests, inhabit saltwater oceans. Some saltwater animals can adapt to brackish or fresh water (freshwater bull sharks and dolphins, for example), but there are no known freshwater sleeper sharks.

Another problem with Wright’s shark-as-lake monster theory is that, despite his suggestion that “the monsters’ shape and colors usually match that of sleeper sharks,” in fact most descriptions of the monsters in Ness and Iliamna bear little resemblance to sleeper sharks. Many eyewitnesses suggest that the unknown aquatic monster in Loch Ness resembles a long-extinct dinosaur-like marine reptile called the plesiosaur.

As for Lake Iliamna, at least one eyewitness reported that Illie had a prominent (3-foot-high) dorsal fin, while sleeper sharks have very low-profile dorsal fins, barely a bump on the back. Researcher Matthew Bille interviewed Illie eyewitnesses for his book Shadows of Existence: Discoveries and Speculations in Zoology, and believes that the most likely explanation for the monster is not a sleeper shark but instead a white sturgeon, which can grow more than 20 feet long: “the appearance of the White sturgeon-gray to brown in color, with huge heads and long cylindrical bodies—appears to match most Iliamna accounts.”

Indeed, it would not be the first time that sturgeon have been mistaken for monsters. Bille notes that “Iliamna has 15 times the volume of Loch Ness. At the same time, it must be admitted there is no physical or film evidence for unknown creatures of any kind.” Such conclusions do not deter Wright; in fact he plans to organize field expeditions to Lake Iliamna and Loch Ness, hoping to find and tag any sleeper sharks he may find there.

You can find more on me and my work with a search for “Benjamin Radford” (not “Ben Radford”) on Vimeo, and please check out my podcast Squaring the Strange!