Flathead Lake
Encyclopedia
Flathead Lake is the largest natural freshwater
lake
in the western part of the contiguous United States
. With a surface area of between 191.5 sq mi (496 km²) and 197 sq mi (510.2 km²), it is slightly larger than Lake Tahoe
. The lake is a remnant of the ancient inland sea
, Lake Missoula of the era of the last interglacial
. Flathead Lake is 27.3 mi (43.9 km) long and up to 15.5 mi (24.9 km) wide. Its known maximum depth is 370.7 ft (113 m), making it deeper than the average depths of the Yellow Sea
or the Persian Gulf
. The lake was raised 10 ft (3 m) by Kerr Dam
. It is one of the cleanest in the populated world for its size and type.
, 7 miles (11 km) south of Kalispell
, it is approximately 30 miles (50 km) long and 16 miles (25 km) wide, covering 191.5 square miles (495.9 km²), making it approximate in size to Minnesota's Mille Lacs Lake and half the area of San Francisco Bay (main bay). Flathead Lake is 30 miles (48 km) southwest of Glacier National Park and is flanked by two scenic highways, which wind along its curving shoreline. On the west side is U.S. Route 93
, and on the east, is Route 35.
The lake is bordered on its eastern shore by the Mission Mountains
and on the west by the Salish Mountains
. The Flathead valley was formed by the glacial damming of the Flathead River
and sustains a remarkably mild climate for a region located this far north and inland; the Pacific Ocean is almost 400 miles to the west. The mild climate allows for cherry orchards on the east shore and vineyards for wine production on the west shore. There are also apple, pear and plum orchards around the lake as well as vegetable, hay, honey, nursery tree, Christmas tree, sod/turf and wheat production bordering or near the lake.
. Kerr Dam
, near Polson
, regulates the lake's water level and provides hydroelectric power and water for irrigation. The lake has an irregularly-shaped shoreline and a dozen small islands, the largest of which is a state park called Wild Horse Island
. These islands cover 5.5 square miles (14.2 square kilometers). Besides the Flathead River
, the Swan River
(known also as the Bigfork River where it enters the lake) is the lake's other major tributary. The lake is inhabited by the native bull trout
and cutthroat trout
, as well as the non-native lake trout
, yellow perch
, and lake whitefish
. It is also reportedly inhabited by the infamous Flathead Lake Monster
.
. The trench
, which formed with the Rocky Mountains
roughly 60 million years ago, extends north into the southern Yukon
as a straight, steep valley
, which also holds the headwaters of the Columbia River
. During the last ice age
this trench was filled by an enormous glacier
. As the glacier moved southward it carved out the trench. Present day Polson, Montana
marks the southernmost extent of the glacier during the last ice age and thus is the site of the glacier's terminal moraine
.
The large size of the Polson Moraine indicates that the glacier stalled here for several years before retreating. As the climate warmed, a portion of the glacier in the Mission Valley receded more slowly than the main body, which kept the lake basin from being filled with sediment. Eventually this ice also melted, forming a lake behind the moraine. Once the water reached the top of this moraine dam
, it began to cut a channel through it. Most moraine dammed lake
s drain quickly because water cuts entirely through the moraine. However, Flathead Lake remains because a bedrock
hill buried underneath the Polson Moraine prevented the moraine from being completely cut through so the meltwater never completely drained.
At one time, probably when the valley was partially filled by a glacier
, the level of Flathead Lake was about 500 feet (150 m) higher and drained through the valley west of Elmo, Montana
which is at the end of Big Arm Bay, bottom center in the aerial photo above. Water carved out a wide, flat-bottomed pass with a deeper, narrow channel at the south edge of the pass. The deeper channel and traces of the dry riverbed are still visible from Route 28.
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
in the western part of the contiguous United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. With a surface area of between 191.5 sq mi (496 km²) and 197 sq mi (510.2 km²), it is slightly larger than Lake Tahoe
Lake Tahoe
Lake Tahoe is a large freshwater lake in the Sierra Nevada of the United States. At a surface elevation of , it is located along the border between California and Nevada, west of Carson City. Lake Tahoe is the largest alpine lake in North America. Its depth is , making it the USA's second-deepest...
. The lake is a remnant of the ancient inland sea
Inland sea
An inland sea is a shallow sea that covers central areas of continents during periods of high sea level that result in marine transgressions. In modern times, continents stand high, eustatic sea levels are low, and there are few inland seas, none larger than the Caspian Sea...
, Lake Missoula of the era of the last interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
. Flathead Lake is 27.3 mi (43.9 km) long and up to 15.5 mi (24.9 km) wide. Its known maximum depth is 370.7 ft (113 m), making it deeper than the average depths of the Yellow Sea
Yellow Sea
The Yellow Sea is the name given to the northern part of the East China Sea, which is a marginal sea of the Pacific Ocean. It is located between mainland China and the Korean Peninsula. Its name comes from the sand particles from Gobi Desert sand storms that turn the surface of the water golden...
or the Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
. The lake was raised 10 ft (3 m) by Kerr Dam
Kerr Dam
Kerr Dam is concrete gravity-arch dam located at river mile 72 of the Flathead River, increasing the size of Flathead Lake near Polson, Montana. The dam was designed for hydroelectricity but also serves recreational uses...
. It is one of the cleanest in the populated world for its size and type.
Geography
Located in the northwest corner of the state of MontanaMontana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, 7 miles (11 km) south of Kalispell
Kalispell, Montana
Kalispell is a city in and the county seat of Flathead County, Montana, United States. The 2010 census put Kalispell's population at 19,927 up 5,704 over 2000. At 40.1% this is the largest percentage of growth of any incorporated city in Montana. Kalispell is the largest city and commercial center...
, it is approximately 30 miles (50 km) long and 16 miles (25 km) wide, covering 191.5 square miles (495.9 km²), making it approximate in size to Minnesota's Mille Lacs Lake and half the area of San Francisco Bay (main bay). Flathead Lake is 30 miles (48 km) southwest of Glacier National Park and is flanked by two scenic highways, which wind along its curving shoreline. On the west side is U.S. Route 93
U.S. Route 93
U.S. Route 93 is a major north–south United States highway in the western United States. The southern terminus is at U.S. Route 60 in Wickenburg, Arizona. The northern terminus is at the Canadian border north of Eureka in Lincoln County, Montana, where the roadway continues into Roosville,...
, and on the east, is Route 35.
Mission Mountains
The Mission Mountains or Mission Range are a range of the Rocky Mountains located in northwestern Montana in the United States. They lie chiefly in Lake County and Missoula County and are south and east of Flathead Lake and west of the Swan Range...
and on the west by the Salish Mountains
Salish Mountains
The Salish Mountains are located in the northwest corner of the U.S. State of Montana....
. The Flathead valley was formed by the glacial damming of the Flathead River
Flathead River
The Flathead River, in the northwestern part of the U.S. state of Montana, originates in the Rocky Mountains near Glacier National Park and flows southwest into Flathead Lake, then after a journey of , empties into the Clark Fork. The river is part of the Columbia River drainage basin, as the Clark...
and sustains a remarkably mild climate for a region located this far north and inland; the Pacific Ocean is almost 400 miles to the west. The mild climate allows for cherry orchards on the east shore and vineyards for wine production on the west shore. There are also apple, pear and plum orchards around the lake as well as vegetable, hay, honey, nursery tree, Christmas tree, sod/turf and wheat production bordering or near the lake.
History
Once known as "Salish Lake", this body of water takes its name from the Salish (Flathead) Indians who live at the southern end of the lake on the Flathead Indian ReservationFlathead Indian Reservation
The Flathead Indian Reservation, located in western Montana on the Flathead River, is home to the Bitterroot Salish, Kootenai, and Pend d'Oreilles Tribes - also known as theConfederated Salish and Kootenai Tribes of the Flathead Nation...
. Kerr Dam
Kerr Dam
Kerr Dam is concrete gravity-arch dam located at river mile 72 of the Flathead River, increasing the size of Flathead Lake near Polson, Montana. The dam was designed for hydroelectricity but also serves recreational uses...
, near Polson
Polson, Montana
Polson is a city in Lake County, Montana, United States, on the southern shore of Flathead Lake. It is also on the Flathead Indian Reservation. The population was 4,041 at the 2000 census. It is the county seat of Lake County...
, regulates the lake's water level and provides hydroelectric power and water for irrigation. The lake has an irregularly-shaped shoreline and a dozen small islands, the largest of which is a state park called Wild Horse Island
Wild Horse Island
Wild Horse Island is the largest island in Flathead Lake, the largest freshwater lake in Montana. For centuries, the Salish-Kootenai used the 2,100 acre island to pasture horses to keep them from being stolen by other tribes...
. These islands cover 5.5 square miles (14.2 square kilometers). Besides the Flathead River
Flathead River
The Flathead River, in the northwestern part of the U.S. state of Montana, originates in the Rocky Mountains near Glacier National Park and flows southwest into Flathead Lake, then after a journey of , empties into the Clark Fork. The river is part of the Columbia River drainage basin, as the Clark...
, the Swan River
Swan River (Montana)
The Swan River in the western part of the U.S. state of Montana starts in the Mission Mountains at Gray Wolf Lake and continues north to Swan Lake. Then it goes west and is impounded by a dam before emptying into Bigfork Bay and the town of Bigfork, where it enters Flathead Lake. The last stretch...
(known also as the Bigfork River where it enters the lake) is the lake's other major tributary. The lake is inhabited by the native bull trout
Bull trout
The bull trout, Salvelinus confluentus, is a char of the family Salmonidae native to northwestern North America. Historically, S. confluentus has been known as the "Dolly Varden" , but was re-classified as a separate species in 1980. Bull trout are listed as a threatened species under the U.S....
and cutthroat trout
Cutthroat trout
The cutthroat trout is a species of freshwater fish in the salmon family of order Salmoniformes. It is one of the many fish species colloquially known as trout...
, as well as the non-native lake trout
Lake trout
Lake trout is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char , touladi, togue, and grey trout. In Lake Superior, they can also be variously known as siscowet, paperbellies and leans...
, yellow perch
Yellow perch
The yellow perch is a species of perch found in the United States and Canada, where it is often referred to by the shortform perch. Yellow perch look similar to the European perch, but are paler and more yellowish, with less red in the fins. They have six to eight dark, vertical bars on their sides...
, and lake whitefish
Coregonus
Coregonus is a diverse genus of fish in the salmon family . The type species is the common whitefish . The Coregonus species are known as whitefishes...
. It is also reportedly inhabited by the infamous Flathead Lake Monster
Flathead Lake Monster
The Flathead Lake Monster is a cryptid, a creature whose existence is not proven, that is said to be located in Flathead Lake in Montana. Its appearance is very similar to that of the Loch Ness Monster, and the two have often been said to be the same type of creature.-Flathead Lake:Flathead Lake...
.
Geology
Flathead Lake lies at the southern end of a geological feature called the Rocky Mountain TrenchRocky Mountain Trench
The Rocky Mountain Trench, or the Trench or The Valley of a Thousand Peaks, is a large valley in the northern part of the Rocky Mountains. It is both visually and cartographically a striking physiographic feature extending approximately from Flathead Lake, Montana, to the Liard River, just south...
. The trench
Trench
A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide , and by being narrow compared to their length ....
, which formed with the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
roughly 60 million years ago, extends north into the southern Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
as a straight, steep valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
, which also holds the headwaters of the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...
. During the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
this trench was filled by an enormous glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
. As the glacier moved southward it carved out the trench. Present day Polson, Montana
Polson, Montana
Polson is a city in Lake County, Montana, United States, on the southern shore of Flathead Lake. It is also on the Flathead Indian Reservation. The population was 4,041 at the 2000 census. It is the county seat of Lake County...
marks the southernmost extent of the glacier during the last ice age and thus is the site of the glacier's terminal moraine
Terminal moraine
A terminal moraine, also called end moraine, is a moraine that forms at the end of the glacier called the snout.Terminal moraines mark the maximum advance of the glacier. An end moraine is at the present boundary of the glacier....
.
Moraine dammed lake
A moraine-dammed lake occurs when a terminal moraine has prevented some meltwater from leaving the valley. Its most common shape is that of a long ribbon .Example of moraine dammed lakes include:*Argentina/Chile: Buenos Aires Lake...
, it began to cut a channel through it. Most moraine dammed lake
Moraine dammed lake
A moraine-dammed lake occurs when a terminal moraine has prevented some meltwater from leaving the valley. Its most common shape is that of a long ribbon .Example of moraine dammed lakes include:*Argentina/Chile: Buenos Aires Lake...
s drain quickly because water cuts entirely through the moraine. However, Flathead Lake remains because a bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
hill buried underneath the Polson Moraine prevented the moraine from being completely cut through so the meltwater never completely drained.
At one time, probably when the valley was partially filled by a glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
, the level of Flathead Lake was about 500 feet (150 m) higher and drained through the valley west of Elmo, Montana
Elmo, Montana
Elmo is a census-designated place in Lake County, Montana, United States. The population was 143 at the 2000 census.-Geography:Elmo is located at ....
which is at the end of Big Arm Bay, bottom center in the aerial photo above. Water carved out a wide, flat-bottomed pass with a deeper, narrow channel at the south edge of the pass. The deeper channel and traces of the dry riverbed are still visible from Route 28.