Question: How long is the river in which Fort Watuaga stood on the shores of?

Context paragraphs:
Fort Beauharnois: Fort Beauharnois was a French fort (or fur post) built on the shores of Lake Pepin, a wide part of the upper Mississippi River, in 1727.  The location chosen was on lowlands and the fort was rebuilt in 1730 on higher ground.  It was the site of the first Roman Catholic chapel in Minnesota, which was dedicated to St. Michael the Archangel.  The fort was named after the Governor of New France at the time, Charles de Beauharnois.

Naval Shipyards, York (Upper Canada): Naval Shipyards, York (Upper Canada) was one of the shipyards of the Royal Navy on Lake Ontario.  The yards was called for by Lieutenant Governor John Graves Simcoe in 1793 and operated from 1798 long before the town of York was populated and up to the War of 1812.  The yard was on the western edge of the town (east of the Fort Rouille) and located south of Front Street on the shores of Lake Ontario west of Bay Street (today the rail tracks south of Union Station).  Ships were built along the sand shores using the trees from the forests inland and launched into Toronto Bay.  While shipbuilding resumed in York (and later in Toronto), the naval yards did not build any other navy ships after 1813 and abandoned and likely moved to a safer and more protected location in Kingston Royal Naval Dockyard.

Mahimangad: Mahimangad Fort (Man T; 17 40' N, 74 25' E; RS.  Koregaon 20 m. W; p. 3,591), in Man lies within the village limits of Sindi Budruk about five and a half miles west of Dahivadi.  The easiest way to it is by the Satara-Pandharpur road to a point about half a mile west of the pass descending into the lower parts of the Man taluka.  From this point a broad track branches off northwards to the fort which lies not more than half a mile from the road.  There are three hamlets close on the north of the fort which towers about 250 feet above them.  It consists of a flat nearly triangular table land with the apex to the east surmounting a perpendicular scarp of black trap below which are steep slopes of short grass with a little soil.  The sides are overgrown in places with prickly pear especially on the north-west corner.  The ascent should be made from the second hamlet which will be encountered on approaching the Pandharpur road from the north-west.  A path about five feet wide with rude steps at intervals of almost every yard takes to the fort.  A steep walk of about five minutes leads up to the gateway, the immediate approach to which is in places almost blocked by prickly pear.  The path which leads up the side in a south-east direction here takes a turn at nearly right angles to the south-west.  But before entering, the visitor will probably go some fifteen yards further to see a small tank cut in the rock, the site of an excellent spring always full of water and furnishing the neighbouring hamlets with their hot weather supply.  The gateway has been cut in the scarp about thirty feet below the summit.  The passage cut is about six feet wide but the gateway narrows to about five feet.  It consisted as usual of a single pointed arch about seven feet high of well cut masonry the top of which has fallen in.  Inside are twenty-two rock-cut steps which wind through a right angle and lead to the top facing east.  The inner side of the curve is as usual protected and the way up the steps proportionately narrowed by a curtain of solid masonry.  On emerging on the top and proceeding east along the north face of the fort on right hand is a small hillock on which stood the office now in ruins.  A little further on is a water tank thirty feet square, originally built of well cut masonry, but now a great deal fallen in.  Near it are two small tanks lined with cement for the storage either of grain or water, and to the south of these is a large pit roughly hewn out of the rock, perhaps intended for prisoners as in Varugad.  About fifty yards further east is a turret of considerable size the masonry of which is solid and on which a gun was planted.  This turret stretches right across the fort but underneath it on the southern side is an archway about four feet high by two broad.  But creeping through it is reached the eastern end which tapers off nearly to a point.  The fort is about a hundred yards long by forty wide.  The walls are about five or six feet high and the masonry, except the top layer, is in fair preservation.  At the east end is one, and at the west end are two bastions at the north-west and south-west angles.  Originally all three were crowned with guns and there are still remains of parapets on them.  On the east bastion is a small stone placed erect for a ling and worshipped as the image of the god Jajarnath Mahadev.  A small fair is held in honour of the god and the existence of this shrine explains how the path up to the fort is in good order.  There is also a ruined building of loose stones near the south-west bastion in honour of some Muhammedan saint or pir.

Florida State Road 31: State Road 31 (SR 31) is a state highway in Southwest Florida in Lee, Charlotte, and DeSoto counties.  It is about 36 miles (58 kilometers) long.  The entire roadway is two lanes wide, even near Fort Myers.  The highway crosses the Caloosahatchee River via the Wilson Pigott Bridge, a small drawbridge, a mile north of the southern terminus.  The northern terminus is with an intersection of SR 70 near Arcadia.  The southern terminus is with an intersection of SR 80 near Fort Myers Shores.  The route is home to G. Pierce Wood Memorial Hospital, replacing the old De Soto Aircraft Field.

Fort Clinton: Fort Clinton (demolished) was one of a pair of American Revolutionary War fortifications located at the confluence of the Popolopen Creek and the Hudson River.  It stood on the south side of Popolopen Gorge, and its companion fort, Fort Montgomery, stood on the north side.  The forts defended a Hudson River Chain that stretched from Fort Montgomery on the west side of the Hudson River to Anthony's Nose on the east side.  The sites of both forts are in present-day Highlands, Orange County, New York.

Boroa: Boroa, is a town in Araucanía, Chile on the shores of Cautín River.  The region near the town south of the Cautin River between the Boroa and Quepe Rivers was the Moluche aillarehue of Boroa.  The site of the town was founded as a Spanish fort "San Ignacio de la Redención" in 1606 by the Maestro de Campo Rodulfo Lisperger during the Arauco War but it did not remain long after he and his garrison were ambushed.  Later in 1649 as a result of the Parliament of Quilín (1647), Martín de Mujica y Buitrón was able to reestablish the fort at Boroa but it was abandoned in 1656 after a long siege during the Mapuche Insurrection of 1655.  One could find vestiges of the old Spanish fort near the mission at its location at the end of the 19th century.

Watauga River: 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.

Apple River Fort: Apple River Fort, today known as the Apple River Fort State Historic Site, was one of many frontier forts hastily completed by settlers in northern Illinois and southern Wisconsin following the onset of the 1832 Black Hawk War.  Located in present-day Elizabeth, Illinois, United States, the fort at the Apple River settlement was built in less than a week.  It was one of the few forts attacked during the war and the only one attacked by a band led by Black Hawk himself.  At the Battle of Apple River Fort, a firefight of about an hour ensued, with Black Hawk's forces eventually withdrawing.  The fort suffered one militia man killed in action, and another wounded.  After the war, the fort stood until 1847, being occupied by squatters before being sold to a private property owner who dismantled the building.

Fort Watauga: Fort Watauga, more properly Fort Caswell, was an American Revolutionary War fort that once stood at the Sycamore Shoals of the Watauga River in what is now Elizabethton, Tennessee.  The fort was originally built in 1775–1776 by the area's frontier government, the Watauga Association, to help defend Watauga settlers from Native American (primarily Cherokee) attacks, which were in part instigated by the British.  Fort Watauga was originally named Fort Caswell after North Carolina Governor Richard Caswell.

Fort Henry (West Virginia): Fort Henry was a fort which stood about ¼ mile from the Ohio River in what is now downtown, Wheeling, West Virginia.  The fort was originally known as Fort Fincastle and was named for Viscount Fincastle, Lord Dunmore, Royal Governor of Virginia.  Later it was renamed for Patrick Henry, and was at the time located in Virginia.  The fort was subject to two major sieges, two notable feats (McColloch's Leap and Betty Zane's trek through the battle) and other skirmishes.

Supporting paragraphs: Fort Watauga Watauga River
Answer: 78.5