drought caused the water in Prospect Reservoir to fall below gravitational flow to the Lower Canal, resulting in a serious water shortage for Sydney's 523,000 inhabitants. The seriousness of the position led the NSW Government, in March 1902, to appoint a Royal Commission to inquire into and report upon the Sydney water supply system. The main recommendation of the Commission was that a storage dam be constructed at a point below the junction of Cataract Creek with the Cataract River. The site was selected as a result of a joint investigation and survey by the staff of the Public Works Department and the Water Board. The survey reports proposed the construction of a dam capable of impounding approximately 7000 million gallons of water, with the option of raising the walls at some future time to allow for the catchment of up to . The Act authorising the construction of the dam was passed in 1902 and provided for a wall of with a storage capacity of . By June 1903, much of the area to be submerged had been cleared of timber, with excavations for the foundations having begun by the end of the year. The contract for the work was let to Messrs Lane and Peters and, by 1905, was well underway with a completion date expected within two years. The contract was for a dam high from the natural flow of the river, which would store up to . During construction, the Minister for Public Works, in a measure of economy, directed that the dam wall be reduced in height by thereby reducing the storage capacity from . The Board however, acting on advice of its President, urged the Minister to have the dam built to its original dimensions. This request was then forwarded to a Royal Commission which, after a full investigation, recommended that the dam be built to its full height and capacity. The work proceeded on this basis and was completed toward the end of 1907 for a total cost of $658,272 and was transferred to the Board on 10 June 1908. The reservoir was filled to capacity for the first time on 13 January 1911, at which time it became obvious that the spillway should be widened to avoid any risk of flood waters overtopping the wall. This work was completed in 1915. In December 2016 the state government gave approval for the controversial