How Wide Is Flathead Lake?

Written by Kyle Glatz
Updated: July 19, 2023
Share on:


Montana has many national parks, remote natural areas, and mountains that residents and visitors love to explore. One of the pastimes that people enjoy in this area is fishing. Fortunately, Montana is rife with lakes and rivers to do just that. Flathead Lake is one of the most well-known lakes in the state. Nature lovers, fishers, and water recreation enthusiasts flock to this lake for a good time.

Infographic of Flathead Lake
Flathead Lake is a favorite place in Montana for those who love nature, fishing, and water recreation.

So, how wide is Flathead Lake? Discover the total width of the lake, how it compares to other wide lakes in the country, and whether the average person could swim across it!

About Flathead Lake

Flathead Lake

Flathead Lake is a large body of water located in the northwestern part of Montana.


Statistics for Flathead Lake
Length27.3 miles
Width15.5 miles
Maximum Depth370 feet
Total Area191.5 square miles

Flathead Lake is in the northwestern part of Montana. Due to its size, portions of the lake span both Lake county and Flathead county. The lake has a total area of 191.5 square miles. That makes this the 79th-largest freshwater lake in the world. The lake has many towns along its shores, including Polson, Finley Point, and Lakeside.

The lake also contains several islands. The largest and most well-known of these islands is Wild Horse Island. Although the horse herds on the island have dwindled in recent years, the island still contains a population of Rocky Mountain bighorn sheep.

Flathead River and Swan River are both tributaries of Flathead Lake. The Flathead River continues to flow out from the southern part of the lake before joining the Clark Fork of the Columbia River. All told, the lake has an exceptionally large catchment area of about 8,587 square miles.

The lake is a very popular destination for tourists. Even during 2020, a year when tourism plummeted, almost 500,000 people traveled to the state park and lake area to enjoy the sights, go fishing, and take part in other recreational activities.

How Wide is Flathead Lake?

Flathead Lake

Flathead Lake stretches over 15 miles at its widest point!


Flathead Lake is 15.5 miles at its widest point. That measure is from just south of the town of Elmo across the lake to where Montana Highway 35 runs along the eastern shore of the lake.

Although Flathead Lake is about half as wide as its maximum width at its northern shores, the lake widens significantly throughout its southern third. However, the southern extremes of the lake only measure about 6.5 miles wide.

Where is Flathead Lake on the Map?

Flathead Lake is in both Lake and Flathead counties in Montana. These counties are in the northwestern part of the state. Finding the lake on a map is as simple as looking at the northeastern part of the Flathead Reservation or following the Flathead River.

No major cities are very close to the lake, but Bigfork has a standing population of nearly 5,000 people. Bigfork, Montana is located along the northeastern part of the Flathead Lake shore where Swan Lake empties into the lake.  

How Flathead Lake Compares to Other Lakes in the U.S.

Grand Marais in Minnesota is located on Lake Superior's north/northwest shore.

Lake Superior is far larger wider and longer than Flathead Lake.


LakeWidthTotal Size
Flathead Lake15.5 miles 191 square miles
Lake Superior159.7 miles31,700 square miles
Great Salt Lake27.96 miles1,699 square miles
Lake of the Woods56 miles1,679 square miles
Iliamna Lake22 miles1,012 square miles

Although Flathead Lake is a sizeable freshwater lake, it does not compare to the largest lakes in North America. In fact, the width of this is not even in the top ten within the country. Given its total size, Flathead Lake is tied for the 30th largest lake in the country by area alone. The other 191-square-mile lake in North America is Lake Tahoe.

Interestingly, Flathead Lake is not the largest lake in the state. That honor belongs to Fort Peck Lake, a 393-square-mile lake in eastern Montana. This reservoir is about 134 miles long. Although it’s not the biggest lake in Montana, Flathead Lake is probably the widest.  

How Long Would It Take Someone to Swim the Flathead Lake’s Width?

Man swimming

Even the best swimmers would have trouble crossing this wide lake.

©l i g h t p o e t/

The average person would not be able to swim across Flathead Lake since it is so wide. However, if someone with a sufficient level of fitness attempted the task, they’d have quite the journey ahead of them. The average swimmer can reach a speed of about 2 mph in the water.

That means they are moving at roughly 2.93 feet per second. The distance they need to cover is 15.5 miles or about 81,840 feet. If the individual was able to maintain the 2.93 feet per second, it would take roughly 465 minutes to swim across the lake, or 7 hours and 45 minutes.

That is a very long, exhausting swim. The chances are high that it would take a much longer time to complete the swim than a mere 7 hours and 45 minutes.  

What Lives in Flathead Lake?

Lake trout fish in hands salvelinus namaycush

Anglers from all over Montana and beyond travel to Flathead Lake to experience the region’s amazing fishing opportunities including lake trout.

©U.S. Fish and Wildlife Service / public domain – License

Anglers from all over Montana and beyond travel to Flathead Lake to experience the region’s amazing fishing opportunities. One reason they enjoy this lake is the variety of native and stocked fish in the waters. Take a look at some of the fish that live in this lake and learn why this lake is so exciting to fishers. The fish in this lake include:

Anglers can catch fish in the deep waters on a boat or from various spots on the shoreline. Some species of fish in the lake can grow quite large. In 2014, a man named Mike Howe caught a 45-inch, 36-pound lake trout. This huge fish set the state record and reminded people why this lake is such a good place to go fishing.

Flathead Lake is one of the largest lakes in Montana as well as one of the widest. This large lake is a beloved spot for people to visit. The sights, small towns, and abundant opportunities for enjoyment in and around the lake make it a desirable place to be. While the area is somewhat remote, a visit to the area would be worth the effort it takes to get there.

The photo featured at the top of this post is © Francisco Blanco/

Share on:
About the Author

Kyle Glatz is a writer at A-Z-Animals where his primary focus is on geography and mammals. Kyle has been writing for researching and writing about animals and numerous other topics for 10 years, and he holds a Bachelor's Degree in English and Education from Rowan University. A resident of New Jersey, Kyle enjoys reading, writing, and playing video games.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.