Since the late 1800s, fishermen and boaters on Flathead Lake have reported sightings of a massive serpentine creature rising from the water. Descriptions vary from a long, eel-like body to something resembling a plesiosaur, often 20–40 feet in length. The earliest accounts date to 1889, when steamboat passengers claimed to see the creature swimming alongside their vessel. Modern sightings continue, with dozens of reports every decade, keeping the Flathead Lake Monster a cornerstone of Montana folklore.