Investigations into where to best build the dam were carried out in two phases. In 1968 and 1974, 24 boreholes and 22 trial pits were sunk before a decision was taken to build the dam at its current height and location rather than further down the valley towards Bury - which would have flooded the hamlet of Hartford.

After a lot of uncertainty and concerns within the village, a decision was made and, on 27th September 1974, the Wimbleball Reservoir Project was inaugurated with Lord Nugent, Chairman of the National Water Council, cutting the turf. The agenda for the official ceremony was published in the Parish News - Inauguration Ceremony for Wimbleball

Building work started in November 1974. Aggregate for the dam concrete came from Holmingham’s Quarry at Cove and the sand came from Hillhead Quarry near Cullompton. This was chosen to give the concrete a pinkish tinge to blend with the surroundings a little better.

At first, the river was diverted through a channel to the North of the central buttresses. It was then diverted over the base of the central buttress until it was finally turned through two 1.2m diameter scour pipes. At one time during its construction, the water level behind the dam rose much higher than intended and water had to be quickly released through the structure.

The dam was finally completed in October 1978 however, owing to a dry winter and demands for water during the summers of 1979 and 1980, the lake did not overflow until November 1980.

According to figures released by South West Water in 1987, the dam cost £16.5 million and stands about 50m high and 300m long holding back 21,562 million litres of water when the reservoir is full - see facts and figures.

During the summer months, there is often a spectacular release of water from the base of the dam to replenish the low water levels of the River Exe which is then extracted at Bolham near Tiverton to supply water to the South West. When the reservoir is particularly low, three pumps located at Exbridge are used to pump water from the River Exe back up to the reservoir at point along the Upton reach. What many people don’t know is that the last 1km of this journey is though a tunnel bored through Haddon Hill.