Flathead Lake

Flathead Lake (Salish: člq̓etkʷ, Kutenai: yawuʔnik̓ ʔa·kuq̓nuk) is a large natural lake in northwest Montana, United States. It is a remnant of an ancient, massive glacial dammed lake called Lake Missoula from the time of the last interglacial era. The lake sits along the main path of the Flathead River.

In 1930, a dam called the Kerr Dam was built at its outlet on Polson Bay, which slightly raised the lake level and helps create electricity. Since 2015, the hydroelectric power from the dam has been owned and operated by the Confederated Salish and Kootenai Tribes. Flathead Lake is known for being one of the cleanest lakes in the populated world for its size and type.

Geography

Flathead Lake is located in the northwest part of Montana, just 7 miles south of Kalispell. The lake is about 30 miles long and 16 miles wide, covering an area of 197 square miles. It is similar in size to Mille Lacs Lake in Minnesota but smaller than Red Lake. Though not as deep as Lake Tahoe, Flathead Lake is deeper than the average depths of the Yellow Sea and the Persian Gulf, with a maximum depth of about 371 feet.

The lake is surrounded by beautiful mountains—the Mission Mountains on the east and the Salish Mountains on the west. The valley where the lake is found was created when glaciers blocked the Flathead River. Despite being far north, the area has a mild climate because it is influenced by air from the Pacific Ocean, almost 400 miles to the west. This mild climate helps grow cherry and apple orchards, vineyards for wine production, and other crops like pear, plum, vegetables, hay, honey, nursery tree, Christmas tree, sod/turf, and wheat.

Flathead Lake has a twisty shoreline with many small islands covering about 5.5 square miles. The largest island is Wild Horse Island, which covers 2,164 acres. Another island, Melita Island, is 64 acres and owned by the Montana Council of the Boy Scouts of America. Since the 1940s, Boy Scouts have used Melita Island for camping and other activities, and they work on projects to help the woodland grow healthier.

Geology

Flathead Lake is found at the southern end of a special area called the Rocky Mountain Trench. This trench formed together with the Rocky Mountains and stretches north into the southern Yukon as a straight, steep valley. During the last ice age, this area was filled with a huge glacier. As the glacier moved south, it shaped the land.

Near the town of Polson, Montana, we can see where the glacier stopped, called the Polson Moraine. This shows how far south the glacier reached during the ice age. The size of this moraine tells us the glacier stayed here for many years before it began to melt away. As the climate got warmer, some of the glacier in the Mission Valley melted slower than the rest. This helped protect the area from being filled with dirt and rocks. Eventually, all the ice melted and created a lake behind the moraine. Flathead Lake stayed because a strong piece of rock under the moraine stopped the water from flowing away completely.

At one time, Flathead Lake was much higher—about 500 feet higher—when the valley was still partly covered by a glacier. The water then flowed out through an area west of Elmo, Montana. You can still see marks of that old river path from Route 28.

Management

The Flathead River and the Swan River are the main rivers that flow into Flathead Lake. Many small streams also add water to the lake, especially along the east shore. The Seli’š Ksanka Qlispe’ Dam, once called Kerr Dam, is located near Polson. This dam helps control the lake's water level, makes electricity, and provides water for farming in the area.

The lake is affected by the Hungry Horse Dam on the South Fork Flathead River. This dam is managed to help fish travel safely to the Columbia River Estuary and the Pacific Ocean. Sometimes, dry weather can make it hard to keep the lake's water level high enough for activities and for fish. In 2023, very low water levels caused problems for businesses and travel on the lake. The following year, plans were changed to help with the dry conditions. In 2025, dry weather again made it difficult to keep the lake full, but unusual rain helped keep the lake near its normal level late in the summer.

History

Flathead Lake used to be called "Salish Lake" because of the Salish Indians who lived nearby. Early European explorers, such as David Thompson, named them the Flathead Indians because they misunderstood some Native American sign language. In 1855, the United States made a treaty called the Treaty of Hellgate, creating the Flathead Reservation just for the Flathead people, which included much of Flathead Lake.

Fauna

Flathead Lake is home to many different kinds of fish, both native and non-native. The lake is managed by Montana Fish, Wildlife and Parks and the Confederated Salish and Kootenai Tribes. Some of the fish you can find there include native species like bull trout and cutthroat trout, as well as non-native fish such as lake trout, yellow perch, and lake whitefish. People have also reported seeing sturgeon and the Flathead Lake Monster in the lake.

Some non-native fish, like the opossum shrimp, were brought into the lake to help produce more kokanee salmon. However, this change affected the lake's ecosystem. The opossum shrimp provided more food for lake trout, which then became very common. This change hurt other fish like kokanee and native bull trout. Efforts like the "Mack Days" fishing contest aim to reduce the number of lake trout and teach people about managing the lake's fish populations.

The lake also has many other fish species, both native and non-native, including cutthroat trout, Northern Pikeminnow, bull trout, Mountain Whitefish, and Westslope Cutthroat Trout, among others. Some of these fish are not actively managed by government agencies.

Panorama