Question: How long is the river on which Wilbur Dam is located?
Context: Wilbur Dam is a hydroelectric dam on the Watauga River in Carter County, in the U.S. state of Tennessee.  It is one of two dams on the river owned and operated by the Tennessee Valley Authority.  The dam impounds Wilbur Lake, which extends for about 3 mi up the Watauga to the base of Watauga Dam.  Completed by 1912 the Ocoee Dam No. 1 is the only Hydroelectric dam that is older, Wilbur Dam was one of the first major hydroelectric projects in Tennessee, and remains one of the oldest dams in the TVA system. Watauga Dam is a hydroelectric and flood control dam on the Watauga River in Carter County, in the U.S. state of Tennessee.  It is owned and operated by the Tennessee Valley Authority, which built the dam in the 1940s as part of efforts to control flooding in the Tennessee River watershed.  At 318 ft , Watauga is the second-highest dam in the TVA river and reservoir system (behind only Fontana), and at the time of its completion was one of the highest earth-and-rock dams in the United States.  The dam impounds the TVA Watauga Reservoir of 6430 acre , and its tailwaters feed into Wilbur Lake.  The Appalachian Trail crosses the top of Watauga 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. The Karcham Wangtoo Hydroelectric Plant is a 1000 MW run-of-the-river hydroelectric power station on the Sutlej River in Kinnaur district of Himachal Pradesh, India.  The dam and power station are located between the villages of Karcham and Wangtoo where the plant also gains its name.  Jaypee Karcham Hydro Corporation Limited of Jaypee Group signed a memorandum of understanding to develop the dam in 1993 and after years of delays, construction on the power station began on 18 November 2005.  In 2015 Jaypee Group sold out Karcham Wangtoo Project to JSW Group. The first generator was commissioned in May 2011, the second in June and the final two in September.  The 98 m tall dam at Karcham ( ) diverts a substantial portion of the Sutlej into a 10.48 m diameter and 17.2 km long headrace tunnel to the underground power station downstream at Wangtoo.  At the station, the water powers four 250 MW Francis turbine-generators before it is sent back into the Sutlej via a 1.2 km long tailrace tunnel.  The difference in elevation between the dam and the power station affords a gross hydraulic head of 298 m .  Water not diverted by the dam is sent over the spillway and down the normal course of the river.  The main spillway is along the crest of the dam and is controlled by six radial gates. Just upstream of the dam is the 300 MW Baspa II Hydroelectric Plant and downstream of the Karcham Wangtoo is the 1,500 MW Nathpa Jhakri 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. The Yunfeng Dam is a concrete gravity dam on the Yalu River which borders China and North Korea.  It is located 33 km northeast of Ji'an in Jilin Province, China and Manpo in Chagang Province, North Korea.  The primary purpose of the dam is hydroelectric power generation and it supports a 400 MW power station.  Construction of the dam had initially began in August 1942 but was halted in 1945 after the surrender of Japan ending World War II.  In October 1959, construction on the dam recommenced and in September 1965, the first of the four 100 MW Francis turbine-generators was operational.  The last generator was operational on 4 April 1967.  The 113.75 m tall dam creates a reservoir with a storage capacity of 3895000000 m3 .  The dam's spillway is an overflow type with 21 floodgates and has a maximum discharge of 21900 m3/s .  The dam is located before a bend in the river and its power station is located on the other side of a ridge that meets the dam’s right abutment.  Water is delivered to the power station via two tunnels, 775 m and 759 m long.  Generators 1 and 3 deliver power to China while 2 and 4 deliver to North Korea. The Diama Dam, sometimes referred to as the Maka–Diama Dam, is a gravity dam on the Senegal River, spanning the border of Senegal and Mauritania.  It is located next to the town of Diama, Senegal and about 22 km north of Saint-Louis, Senegal.  The purpose of the dam is to prevent saltwater intrusion upstream, supply water for the irrigation of about 45000 ha of crops and create a road crossing for the road between St. Louis and Nouakchott in Mauritania.  Additionally, a ship lock built within the dam provides for navigation upstream.  Plans for the dam were first drawn in 1970 when the riparian states within the Senegal River Basin Development Authority agreed to develop the Senegal River.  The Diama Dam was to be constructed in conjunction with the Manantali Dam which was to be located further upstream in Mali.  Construction on the Diama Dam began on 15 September 1981 and was completed on 12 August 1986.  The Manantali Dam was completed in 1988.  The Diama project was funded by a US$149.5 million loan from the African Development Bank.  The main section of the dam with ship lock and spillway is 170 m long while a 440 m long embankment dam section extends north to the edge of the river.  A dike further extends the dam to the north.  The dam is 18 m tall and it is spillway has a maximum discharge of 6500 m3/s . The Watauga River is a large stream of western North Carolina and East Tennessee.  It is 78.5 mi long with its headwaters on the slopes of Grandfather Mountain and Peak Mountain in Watauga County, North Carolina. The Longshou II Dam, also referred to as Longshou No. 2, is a concrete-face rock-fill dam on the Heihe River, located 35 km southwest of Zhangye in Gansu Province, China.  It is part of the Gansu Heihe Rural Hydropower Development and supports a 157 MW power station.  The dam's first feasibility study was carried out in 2000 and river diversion construction began in December 2001.  In June 2002, the river was diverted and in September that year, filling of the dam's body began.  On 17 August 2004, the first generator was operational with the rest by the end of the year.  The 146.5 m high dam withholds a reservoir with a capacity of 86200000 m3 .  It's spillway is located on the right bank and is a controlled chute type with a discharge capacity of 2696 m3/s .  Water is delivered to the dam's power station downstream via a 1.7 km long tunnel.  The dam is located upstream of the Longshou I Dam, an 80 m tall double-curvature arch dam with an installed capacity of 52 MW. Lock and Dam No. 15 is a lock and dam located on the Upper Mississippi River.  It spans the river between Rock Island, Illinois and Davenport, Iowa.  Lock and Dam 15 is the largest roller dam in the world, its dam is 1203 ft long and consists of nine 109 ft non-submersible, non-overflow roller gates and two 109 ft non-submersible overflow roller gates.  It is unusual among the upper Mississippi River dams in that it has only roller gates, has different sizes and types of roller gates, it is not perpendicular to the flow of the river and is one of the few facilities that has a completed auxiliary lock.  The main lock is 110 ft wide by 600 ft long and its auxiliary lock is 110 ft wide by 360 ft long.  In 2004, the facility was listed in the National Register of Historic Places as Lock and Dam No. 15 Historic District, #04000175 covering 3590 acre , 2 buildings, 9 structures, and 1 object.
Answer: 78.5 mi