Question: Milner Dam impounds a river that is how long?

full_context: Document 1: Kootenay River: The Kootenay (Kootenai in the U.S. and historically called the Flatbow) is a major river in southeastern British Columbia, Canada and northern parts of the U.S. states of Montana and Idaho. It is one of the uppermost major tributaries of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. The Kootenay River runs 781 km from its headwaters in the Kootenay Ranges of the Canadian Rockies, flowing from British Columbia's East Kootenay region into northwestern Montana, thence into northernmost Idaho Panhandle and returning to British Columbia in the West Kootenay region, where it joins the Columbia at Castlegar.
Document 2: Imnaha River: The Imnaha River is a 73.3 mi tributary of the Snake River in the U.S. state of Oregon. Flowing generally east near the headwaters and then north through Wallowa County, the entire river is designated Wild and Scenic. It follows a geologic fault to the Snake River, and in addition to land in the Wallowa–Whitman National Forest and private land, its corridor includes parts of three special management areas: the Eagle Cap Wilderness, Hells Canyon National Recreation Area, and Hells Canyon Scenic Byway. The Imnaha flows by the unincorporated community of Imnaha, the only settlement along its course, and enters the Snake River roughly 4 mi from the larger river's confluence with the Salmon River of Idaho and 192 mi from its confluence with the Columbia River.
Document 3: Snake River: The Snake River is a major river of the greater Pacific Northwest in the United States. At 1078 mi long, it is the largest tributary of the Columbia River, the largest North American river that empties into the Pacific Ocean. Rising in western Wyoming, the river flows through the Snake River Plain of southern Idaho, then through the rugged Hells Canyon area via northeastern Oregon and the rolling Palouse Hills, to reach its mouth near the Washington Tri-Cities area, where it enters the Columbia. Its drainage basin encompasses parts of six U.S. states, and its average discharge is over 54000 cuft/s .
Document 4: Milner Dam: Milner Dam is a rockfill dam near Burley in south central Idaho. It impounds the Snake River in a reservoir named Milner Lake. The dam spans the river across two islands, with three embankments.
Document 5: Snake River Aquifer: The Snake River Aquifer is a large reservoir of groundwater underlying the Snake River Plain in the southern part of the U.S. state of Idaho. Most of the water in the aquifer comes from rain and melting snow that flows onto the plain from the Snake River, Big Lost River, Bruneau River, and other watercourses of southern Idaho. Measuring about 400 mi from east to west, it is an important water source for agricultural irrigation in the Plain. The Snake River Aquifer is commonly defined as two separate parts, separated by Salmon Falls Creek. These are the Eastern Snake River Plain Aquifer and Western Snake River Plain Aquifer.
Document 6: Culmback Dam: The Culmback Dam (also known as the George Culmback Dam or the Snoqualmie National Forest Dam) is a large rockfill hydroelectric and water supply dam on the Sultan River, a tributary of the Skykomish River, in Washington. Built in 1965, the dam is 640 ft long at the crest and 262 ft high. Its reservoir, Spada Lake, provides water for 70 to 75 percent of Snohomish County, and the powerhouse downstream of the dam produces 112 megawatts. Some critics charge that the dam has strongly impacted the runs of salmon and other migratory fish in the Sultan River by depleting gravel and sediment needed to line the riverbed. The dam’s operator counters that Culmback Dam dramatically reduces flooding events, benefiting fish populations and the surrounding communities. The dam was named in honor of George Culmback, a former mayor of Everett.
Document 7: 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. It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is 1243 mi long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province. The fourth-largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific.
Document 8: Clark Fork River: The Clark Fork, or the Clark Fork of the Columbia River, is a river in the U.S. states of Montana and Idaho, approximately 310 mi long. The largest river by volume in Montana, it drains an extensive region of the Rocky Mountains in western Montana and northern Idaho in the watershed of the Columbia River. The river flows northwest through a long valley at the base of the Cabinet Mountains and empties into Lake Pend Oreille in the Idaho Panhandle. The Pend Oreille River in Idaho, Washington, and British Columbia, Canada which drains the lake to the Columbia in Washington, is sometimes included as part of the Clark Fork, giving it a total length of 479 mi , with a drainage area of 25820 sqmi . In its upper 20 mi in Montana near Butte, it is known as Silver Bow Creek. Interstate 90 follows much of the upper course of the river from Butte to northwest of Missoula. The highest point within the river's watershed is Mount Evans at 10641 ft in Deer Lodge County, Montana along the Continental Divide.
Document 9: Kingsley Dam: Kingsley Dam is located on the east side of Lake McConaughy in central Keith County, Nebraska, and is the second largest hydraulic fill dam in the world. It was built as part of the New Deal project. The dam is 162 ft tall, 3.1 mi long, and 1100 ft wide at its base. On the east side of the dam is Lake Ogallala and on the south side is the Kingsley Hydroelectricity Plant. The Nebraska Game and Parks Commission and Central Nebraska Public Power and Irrigation District are also located in this area. Kingsley Dam, the Kingsley Hydroelectricity Plant, the Morning Glory Spillway, and the Outlet Tower – a large structure near the dam used to release water from the lake – are main visual icons of Lake McConaughy.
Document 10: Hoback River: The Hoback River, also called the Fall River , is an approximately 55 mi -long tributary of the Snake River in the U.S. state of Wyoming. It rises in the northern Wyoming Range of Wyoming and flows northeast through the Bridger-Teton National Forest, before turning northwest to join the Snake just downstream of Jackson Hole, near the head of the Snake River Canyon and near the town of Hoback. The largest tributary of the Hoback River is its South Fork, which joins it near the town of Bondurant, where the river spreads onto a large marshy flat in a braided floodplain once known as Jackson's Little Hole., but now referred to as the "Hoback Basin". However, most of the river flows through narrow valleys and in its lower course, steep mountain canyons. The entire length of the Hoback is free flowing and unobstructed by dams. About 30 mi downstream from the confluence with the Hoback River, the Snake River crosses into the state of Idaho and is impounded by Palisades Dam.
Document 11: Lake Red Rock (Des Moines River): Originally the city of Red Rock, Lake Red Rock, also referred to as Red Rock Reservoir is a reservoir formed by Red Rock Dam on the Des Moines River, about 55 miles southeast of the city of Des Moines, Iowa, United States. The dam was completed in 1969 as a flood control project by the United States Army Corps of Engineers, creating the largest lake in Iowa. The lake is essentially confined to Marion County. The damface is a few miles west and south of Pella, and similarly, a few miles northeast of Knoxville.
Document 12: Bruno Creek Tailings Impoundment: The Bruno Creek Tailings Impoundment is a tailings dam on Bruno Creek, 19 mi southwest of Challis in Custer County, Idaho. It serves to store tailings for the nearby Thompson Creek Mine. At 550 ft tall, it is the second tallest center-line tailings dam in the world. In 2008, Phase 8 of the mine was approved which includes a raising of the dam to 750 ft . The dam is mainly composed of cycloned sand. Currently, the dam stores 100000000 MT of tailings and the raise would increase storage to 125000000 MT . The downstream slope of the dam will be steepened from 3:1 to 2.75:1. In 1994, it was discovered that acid mine drainage had been forming on the embankment since 1987. Since seepage does occur at the dam, a system of wells was installed to monitor groundwater and a seepage return dam was constructed downstream.
Document 13: Nine Mile Dam: Nine Mile Falls Dam is a dam on the Spokane River, in the unincorporated community of Nine Mile Falls, Washington. It was built on the site of the falls in 1908, creating Nine Mile Reservoir. The dam was designed by the New York engineering firm of Sanderson & Porter, and originally constructed to satisfy the power needs of the Spokane and Inland Empire Railroad interurban trolley lines.
Document 14: Snake River Range: The Snake River Range is located in the U.S. states of Wyoming and Idaho and includes 10 mountains over 9000 ft . The tallest peak in the range is Mount Baird at 10025 ft . The range trends northwest to southeast and is bordered on the north by the Teton Range and the two ranges meet at Teton Pass. The Snake River Range is bordered by the Palisades Reservoir to the west and the Snake River, which sweeps completely around the eastern, southern and western part of the range. The range is approximate 30 mi north to south and 33 mi west to east, covering 528 sqmi . Along the southern boundary, the Snake River passes through Grand Canyon, also known as the Snake River Canyon. U.S. Route 26/U.S. Route 89 follows the course of the Snake River from Hoback Junction to the Palisades Reservoir.
Document 15: Hume Dam: Hume Dam, formerly the Hume Weir, is a major dam across the Murray River downstream of its junction with the Mitta River in the Riverina region of New South Wales, Australia. The dam's purpose includes flood mitigation, hydro-power, irrigation, water supply and conservation. The impounded reservoir is called Lake Hume, formerly the Hume Reservoir. It is a gated concrete gravity dam with four earth embankments and twenty-nine vertical undershot gated concrete overflow spillways.
ground_truth: 1078 mi