of the dam. Ownership of the reservoir passed to the Yorkshire Water Authority in 1974, and following the passing of the Water Act 1989 and the privatisation of the water companies, it has been owned by Yorkshire Water. The reservoir covers , the earth embankment that forms the dam is long and a maximum of high, and it impounds over of water. A new treatment works to replace those at Langsett and Midhope was constructed between 1983 and 1985, and can treat 60 Megalitres of water per day. It supplies drinking water to south-west Barnsley and north-west Sheffield. A little further downstream, the Little Don is joined by Hagg Brook, a small stream that is fed by the overflow from Midhope Reservoir. There is another weir in the Little Don at Midhopestones, just before Midhopestones Bridge. This small bridge carried Mortimer Road over the river, and is constructed of coursed gritstone blocks. It has three arches, a large one in the centre and a smaller one at either side. It dates from 1788 and is grade II listed. Underbank Reservoir begins immediately below the bridge. While Langsett and Midhope reservoirs are used for water supply, Underbank provides compensation water for the Little Don and the Don. The volumes of water released were thought to be too high in 2017, as they had historically supplied the many industrial sites further down the Don. There is a spillway from the southern edge of the dam with a weir at the bottom, after which the river is crossed by Unsliven Bridge. A bridge was mentioned at this location in a charter which pre-dates 1290. The bridge that now stands there was erected around 1730, with a main arch and a smaller arch in the north abutment. It formed part of the route between Bradfield and Wakefield, on which traffic increased significantly during the industrial revolution. It was widened twice in the 18th century, and by 1796 was twice as wide as it had been. The northern approach was realigned in 1805, when the bridge became part of the Langsett, Wadsley, and Sheffield Turnpike. A toll bar was erected near the bridge, but was removed in 1838 when the Turnpike was repealed by Act of Parliament. The road to the north of the bridge was realigned as part of the work to build the reservoir dam. It has only been used by local traffic