Plans for the building of the reservoir were under discussion before the Second World War, and an Act of Parliament submitted by the Bristol Waterworks Company was passed in 1939. Following this, farms were bought by the company and farmed by the previous owners as tenancies. Farms and buildings still remaining in private hands were acquired by compulsory purchase. The sanction for construction was given in 1949 and the contract awarded to A.E. Farr, who employed 300 people on the site. The main dam was stabilised by injecting concrete into the cracks in the bedrock. The core of the dam was made of puddled clay mixed with sand. This was the first time the gain in strength brought about by the use of sand drains had been quantified.[12] The lake was inaugurated by Queen Elizabeth II, accompanied by Prince Philip, with the unveiling of a commemorative stone and plaque, which can be seen from the dam, on 17 April 1956, although it was not full until 25 February 1958.[8] Flowers were presented to the Queen at the opening of Chew Valley Lake by Judith Blair Brown, daughter of Kennedy Brown, who worked at Bristol Water Works at the time of construction of the lake.
