The story of a monster in Flathead Lake originates in a Kutenai traditional legend. According to the story, long ago, the first native tribe in the area lived on an island in the middle of the lake. One winter while crossing the frozen lake to move camp, two girls saw antlers approximately two feet in length protruding through the frozen ice. Thinking the antlers belonged to some animal, the girls decided to chop them off and take them. They used sharp-edged rocks to cut through the ice when the antlers suddenly started shaking, the ice around them split open, and the head of a monster appeared through the ice shaking its giant antlers. The girls used their special powers to transform into a ball and a buckskin target to escape the monster, but half of the tribe drowned in the lake, which is said to be the reason why there are so few Kutenai people. The narrative holds that the Kutenai never strayed far from the lakeshore after that, and white settlers later reported occasionally seeing the monster.
Local tales of the Flathead Lake Monster go back more than 100 years. It was supposedly first reported in 1889 by Captain James C. Kerr of the lake steamboat the U.S. Grant who claimed he and his 100 passengers saw an unusually large whale-like object in the water. According to the story, one of the passengers on the steamer shot at the creature and sent it diving for safety. Contemporary reports of sightings by local residents and visitors average between one and two each year.
One local story that received much publicity described how a 3-year old boy apparently fell into the lake, and when asked how he had extracted himself, told his mother “The Flathead monster lifted me up”. In the 1950s, a significant cash reward was offered by Big Fish Unlimited to anyone who could catch what was termed the “superfish” of Flathead Lake. A man named C. Leslie Griffith was reported to have caught a 7-foot, 6-inch, 181-pound, 1-ounce white sturgeon, now displayed at the Polson-Flathead Historical Museum.