Question: What Montana river was a dam built on under the Columbia River Treaty?

Context paragraphs:
Pend Oreille River: The Pend Oreille River is a tributary of the Columbia River, approximately 130 mi long, in northern Idaho and northeastern Washington in the United States, as well as southeastern British Columbia in Canada.  In its passage through British Columbia its name is spelled Pend-d'Oreille River.  It drains a scenic area of the Rocky Mountains along the U.S.-Canada border on the east side of the Columbia.  The river is sometimes defined as the lower part of the Clark Fork, which rises in western Montana.  The river drains an area of 66800 km2 , mostly through the Clark Fork and its tributaries in western Montana and including a portion of the Flathead River in southeastern British Columbia.  The full drainage basin of the river and its tributaries accounts for 43% of the entire Columbia River Basin above the confluence with the Columbia.  The total area of the Pend Oreille basin is just under 10% of the entire 258000 mi2 Columbia Basin.  Box Canyon Dam is currently underway on a multi million dollar project for a fish ladder.

Bonneville Dam: Bonneville Lock and Dam consists of several run-of-the-river dam structures that together complete a span of the Columbia River between the U.S. states of Oregon and Washington at River Mile 146.1.  The dam is located 40 mi east of Portland, Oregon, in the Columbia River Gorge.  The primary functions of Bonneville Lock and Dam are electrical power generation and river navigation.  The dam was built and is managed by the United States Army Corps of Engineers.  At the time of its construction in the 1930s it was the largest water impoundment project of its type in the nation, able to withstand flooding on an unprecendented scale.  Electrical power generated at Bonneville is distributed by the Bonneville Power Administration.  Bonneville Lock and Dam is named for Army Capt. Benjamin Bonneville, an early explorer credited with charting much of the Oregon Trail.  The Bonneville Dam Historic District was designated a National Historic Landmark District in 1987.

Lake Sherburne Dam: Lake Sherburne Dam is a 107 ft high compacted earthfill dam built between 1914 and 1921 built just outside the boundary of Glacier National Park, Montana, its reservoir extending into the park.  The dam impounds Swiftcurrent Creek as it flows out of the park.  Water stored in Lake Sherburne is released to flow down Swiftcurrent Creek to the St. Mary River, from which it is diverted to the Milk River, flowing through Canada for 216 mi before returning to the United States.  Use of these waters is governed by the Boundary Waters Treaty of 1909.  Water from the Milk River is used for irrigation in north central Montana.

Dry Falls Dam: Dry Falls Dam is a rockfaced earthfill type dam in the U.S. state of Washington.  Located in Grant County near Coulee City, it was built as part of the Bureau of Reclamation's Columbia Basin Project.  Water from the Columbia River, impounded by Grand Coulee Dam, is pumped into Grand Coulee, a formerly dry canyon, through the short Feeder Canal.  Grand Coulee's north end is sealed by North Dam and Dry Falls Dam stretches across the midsection of the Coulee.  This allows the water pumped from the Columbia River to fill the upper Grand Coulee, creating a large equalizing reservoir known as Banks Lake.  Water from the reservoir is fed into the irrigation project's Main Canal, which runs south from Dry Falls Dam to another reservoir called Billy Clapp Lake, formed by Pinto Dam.

Nam Ngum Dam: The Nam Ngum Dam is a hydroelectric dam on the Nam Ngum river, a major tributary of the Mekong in Laos.  It was the first hydropower dam built in Lao PDR.  It was constructed in three stages, beginning in with stage I in 1968 and ending with the completion of stage III in 1984.  The Mekong Commission first implemented the dam project as part of the national development plan.  The project was mainly focused on harnessing Lao PDR’s hydropower potential, but it has also striven to achieve flood protection, implement lift irrigation, facilitate lake fishery, and develop Lao PDR’s tourism industry.  The Nam Ngum Dam has a capacity of 155MW and generates most of Laos' electricity, including all the power used in the capital, Vientiane.  Additionally 70% to 80% of electricity created by the dam is exported to Thailand.  The revenue from this exporting accounts for about a quarter of Laos' foreign exchange earnings.  The gross power revenues of the dam are approximately US$36 million annually.  However, recent studies have insinuated that the dam has adversely affected lake fishery and the wider Nam Ngum river ecosystem.  Responsibility for operation of the project rests with the national power utility Electricité du Laos, a state enterprise under the Ministry of Industry and Handicraft.

Libby Dam: Libby Dam is a dam on the Kootenai River in the U.S. state of Montana.

Boat Encampment: Boat Encampment was a rendezvous and staging point for the Hudson's Bay Company in the early 19th century and later a locality by that name in the Canadian province of British Columbia.  It was located at the "top" of the Big Bend of the Columbia north of the city of Revelstoke, British Columbia and southeast of Valemount.  Its site today is beneath the waters of Kinbasket Lake Reservoir, formed by the Mica Dam of the Columbia River Treaty.

Columbia River Treaty: The Columbia River Treaty is a 1964 agreement between Canada and the United States on the development and operation of dams in the upper Columbia River basin for power and flood control benefits in both countries.  Four dams were constructed under this treaty: three in British Columbia, Canada (Duncan Dam, Mica Dam, Keenleyside Dam) and one in Montana in the United States (Libby Dam).  The treaty provided for the sharing with Canada of one-half of the downstream U.S. power and flood benefits, and allows the operation of Treaty storage for other benefits.  The long-term impacts of the treaty have been mixed: while the dams have provided enormous economic benefits to British Columbia and the U.S. Pacific Northwest through hydroelectric generation and flood control, there are longstanding concerns regarding social and economic impacts to the local communities, and the environmental effects associated with the construction and operation of large dams.

Mica Dam: Mica Dam, a hydroelectric dam spanning the Columbia River 135 kilometres north of Revelstoke, British Columbia, Canada, was built as one of three Canadian projects under the terms of the 1964 Columbia River Treaty and is operated by BC Hydro.  Completed in 1973 under the terms of the treaty, the Mica powerhouse had an original generating capacity of 1,805 megawatts (MW).  Mica Dam, named after the nearby settlement of Mica Creek and its associated stream, in turn named after the abundance of mica minerals in the area, is one of the largest earthfill dams in the world.  The reservoir for the dam is Kinbasket Lake, which was created when the dam was built.  Water from the dam flows south directly into Revelstoke Lake, the reservoir for the Revelstoke Dam.  Mica Dam is the tallest dam in Canada and second tallest in North America after the Chicoasén Dam in Mexico and it is the farthest upstream dam on the Columbia River.  The dam's underground powerhouse was the second largest in the world at the time of its construction, and was the first 500 kV installation of sulphur hexafluoride (SF) insulated switchgear in the world.

Black Eagle Dam: Black Eagle Dam is a hydroelectric gravity weir dam located on the Missouri River in the city of Great Falls, Montana.  The first dam on the site, built and opened in 1890, was a timber-and-rock crib dam.  This structure was the first hydroelectric dam built in Montana and the first built on the Missouri River.  The dam helped give the city of Great Falls the nickname "The Electric City."  A second dam, built of concrete in 1926 and opened in 1927, replaced the first dam, which was not removed and lies submerged in the reservoir.  Almost unchanged since 1926, the dam is 782 ft long and 34.5 ft high, and its powerhouse contains three turbines capable of generating seven megawatts (MW) of power each.  The maximum power output of the dam is 18 MW.  Montana Power Company built the second dam, PPL Corporation purchased it in 1997 and sold it to NorthWestern Corporation in 2014.  The reservoir behind the dam has no official name, but was called the Long Pool for many years.  The reservoir is about 2 mi long, and has a storage capacity of 1,710 acre.ft to 1,820 acre.ft of water.

Supporting paragraphs: Columbia River Treaty Libby Dam
Answer: Kootenai River