Largest lakes & reservoirs in Montana by water volume
The estimated volume of water that a lake contains is measured at the lake’s normal elevation. By this measure, the world’s largest freshwater lake is Siberia’s Lake Baikal.Water Volume can be measured in acre-feet, in cubic miles, or in cubic kilometers. One acre-foot is the amount of water needed to cover one acre (43,560 square feet) to a depth of one foot. One cubic mile equals 3,379,200 acre-feet. One cubic kilometer equals 810,713 acre-feet. 1 acre-foot is equal to 325,851 US gallons. Siberia’s Lake Baikal contains about 6,276,367,740,000,000 gallons of freshwater – nearly 1 million gallons for every living person on earth.
The other – and more widely used – measure of a lake’s size is the lake’s surface acreage. By that measure, the world’s largest freshwater lake is North America’s Lake Superior.
Note: In the United States, an acre foot is a unit of volume used to refer to large-scale bodies of water. It is defined by the volume of water needed to cover 1 acre of surface area to a depth of 1 foot.
You can find many of the the world’s largest lakes (by water volume) on LakeLubbers. Note: For some lakes, the water volume data is unknown or does not apply, so you may see fewer lakes than the total 30 articles we have published for Montana lakes.
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Below are lakes within USA > US West Region > Montana > Compared by water volume. This list does not represent all lakes in Montana, only the 30 Montana lake articles we have published on the LakeLubbers website.
Lake name  |
Water vol. in ac-ft |
Lake description |
|---|---|---|
| Fort Peck Lake, MT (Missouri River Country, MT, Montana, US West Region, USA) |
18,700,000 ac-ft | Fort Peck Lake, located 20 miles southeast of Glasgow, Montana on Montana Highway 24, is the 5th-largest man-made reservoir by volume in the United St… |
| Lake Koocanusa, MT / Canada (British Columbia, Canada, Canada, Glacier Country, MT, Montana, US West Region, USA) |
5,850,000 ac-ft | (Also known as Koocanusa Lake, Koocanusa Reservoir) In the far north of the United States, tucked into the northwestern end of Montana, is the long, narrow Lake Koocanusa. This lake is actually a man-ma… |
| Hungry Horse Reservoir (Glacier Country, MT, Montana, US West Region, USA) |
3,468,000 ac-ft | Hungry Horse Reservoir in Montana’s Glacier Country offers a wealth of recreational opportunities to northwestern Montana visitors. The nearly 24,000-… |
| Canyon Ferry Lake, MT (Gold West Country, MT, Montana, US West Region, USA) |
1,891,888 ac-ft | For lake lovers who relish the beauty of nature and the wonder of wildlife, there’s no better place to relax and have fun than at Canyon Ferry Lake. A… |
| Flathead Lake, MT (Glacier Country, MT, Montana, US West Region, USA) |
1,200,000 ac-ft | Carved out by the historic glaciers of the last ice age approximately 11,000 years ago, Flathead Lake is one of the largest natural freshwater lakes i… |
| Hebgen Lake (Gold West Country, MT, Montana, US West Region, USA, Yellowstone Country, MT) |
386,000 ac-ft | Anglers will find some of Montana’s best stillwater trout fishing at Hebgen Lake. The 12,500-acre reservoir lies conveniently just outside the western… |
| Bowman Lake, MT (Glacier Country, MT, Montana, US West Region, USA) |
174,469 ac-ft | Bowman Lake is located in the northwest corner of scenic Waterton-Glacier International Peace Park. The crystal clear waters of Bowman Lake reflect th… |
| Swan Lake MT (Glacier Country, MT, Montana, US West Region, USA) |
171,654 ac-ft | Montana conjures images of snow-capped mountains and clean waters full of fish, and Swan Lake more than lives up to that reputation. Surrounded by the… |
| Ennis Lake (Gold West Country, MT, Montana, US West Region, USA) |
27,200 ac-ft | In 1905 the Montana Power Company built a dam on the Madison River, creating Ennis Lake. The two and a half mile long lake stretches across Montana’s… |
| Mystic Lake (Montana, US West Region, USA, Yellowstone Country, MT) |
21,000 ac-ft | One of the prettiest lakes in Montana’s Yellowstone Country is Mystic Lake. This beautiful lake sits at 7,637 feet above sea level in the Absaroka-Bea… |
| Echo Lake MT (Glacier Country, MT, Montana, US West Region, USA) |
11,815 ac-ft | Tiny islands, curving coves and wide bays are part of the allure of northern Montana’s Echo Lake. Coupled with mountains, wildlife, and the smell of t… |