Haweswater is a reservoir in the English Lake District, built in the valley of Mardale in the county of Cumbria. The controversial construction of the Haweswater dam started in 1929, after Parliament passed an Act giving the Manchester Corporation permission to build the reservoir to supply water for the urban conurbations of north-west England. At the time, there was public outcry about the decision, as the valley of Mardale was populated by the farming villages of Measand and Mardale Green and the construction of the reservoir would mean that these villages would be flooded and lost and the population would have to be moved. In addition, the valley was considered one of the most picturesque in Westmorland and many people thought it should be left alone.
Originally, Haweswater was a natural lake about four kilometres long, almost divided in two by a tongue of land at Measand; the two reaches of the lake were known as High Water and Low Water. The building of the dam raised the water level by 29 metres (95 feet) and created a reservoir six kilometres (four miles) long and around 600 metres (almost half a mile) wide. The dam wall measures 470 metres long and 27.5 metres high; at the time of construction it was considered to be cutting-edge technology as it was the first hollow buttress dam in the world, being constructed using 44 separate buttressed units joined by flexible joints. There is a parapet, 1.4 metres (56 inches) wide, running the length of the dam and from this, tunnelled supplies can be seen entering the reservoir from the adjoining valleys of Heltondale and Swindale. When the reservoir is full, it holds 84 billion litres (18.6 billion gallons) of water. The reservoir is now owned by United Utilities plc.