The Flathead Lake Monster, also known as “Flessie,” is a legendary lake monster that is said to live in Flathead Lake which is the largest natural freshwater lake in the western United States (outside of Alaska). It is often compared to other lake monsters such as the Loch Ness Monster.
Cryptid Name: | Flathead Lake Monster (Flessie) |
Location: | Flathead Lake, Montana, USA![]() |
Category: | Aquatic Cryptid |
Description: | A large, serpentine creature with humps or coils. |
Size: | Varies – Between 20 to 40 feet (6 to 12 meters) long. |
Behavior/Characteristics: | Said to exhibit serpentine movement in the water, occasionally showing humps or undulations. Some witnesses have reported seeing the creature swimming, diving, or breaching the surface of the water. |
Diet: | Unknown, although likely fish and lake vegetation. |
Habitat/Environment: | The deep waters of Flathead Lake, a large freshwater lake. |
Evidence: | Limited and largely anecdotal; no conclusive scientific evidence supporting its existence. |
Sightings and Encounters: | Numerous anecdotal reports of sightings and encounters over the years by locals and visitors. |
Skepticism/Explanations: | Skeptics suggest misidentifications of existing animals such as a large fish, such as a sturgeon or a lake trout; logs, waves, or other natural phenomena. Lack of photographic or physical evidence raises doubts. |
Flathead Lake Monster Description

The Flathead Lake Monster, also affectionately known as “Flessie” by locals, is an elusive lake monster that is said to live in Flathead Lake in Montana. Eyewitnesses describe it as being from about 20 to 40 feet (6 to 12 meters) long with a brownish to blue-black color. It is long and slender and resembles a snake or eel with many witnesses saying that they have seen humps or coils above the service of the water.
While investing the Flathead Lake Monster I found the following really interesting video. While this is not a video of the Flathead Lake Monster, it does look very similar to the sightings that many people report so I wanted to include it here as it is one of the few videos that is crisp and clear.
Flathead Lake Monster Sightings

Source: The Flathead Lakers
There are over 120 sightings that have been recorded for the Flathead Lake Monster over the years going all the way back to 1889. Sightings that have been recorded have all come from credible witnesses with different backgrounds including sailing instructors, fish biologists, lawyers, policemen, and ordinary people visiting the lake. All the reported sightings have also been very consistent which suggests a common experience more than random stories.
In general, there are one or two sightings a year with the highest number of reported sightings being in 1993 when there were 13 unusual sightings that year.
Over the years there have been various investigations done to gather evidence including sonar scans and underwater searches but unfortunately, no definitive proof has been found to prove that the Flathead Lake Monster is real.
Regardless of whether it is real or not, the Flathead Lake Monster is an incredibly popular legend in Montana and it has been featured in books and television shows. It also is a very popular tourist attraction bringing visitors to the area who hope to catch a glimpse of the monster.
Theories and Explanations
Of course, just like most cryptids, there are many skeptics who doubt the existence of the Flathead Lake Monster. Some common explanations for its sightings include:
- Misidentifications of large fish such as sturgeon or lake trout.
- A natural phenomenon such as a log or wave.
- A real creature that has not been identified by science yet.
- An elaborate hoax.
- A pre-historic dinosaur that still survives today (such as a plesiosaur).

Source: Popular Science Monthly Volume 53
Similar Cryptids
- Colossal Claude – Oregon
- Coosa River Monster – Alabama/Georgia
- Hawkesbury River Monster – Australia
- Bessie of Lake Erie – United States