the flows through Ohau A do not have to be exactly matched to those through Ohau B and Ohau C. Construction Before construction of the dam could start the Ōhau River was diverted by cutting a channel through a low, rocky extension of the Benmore Range and building three diversion gates there which consumed 200,000 cubic metres of concrete. The Ōhau River was diverted in August 1980 so that water passed through Ohau A and then back down the river bed. Later that year, downstream of Ohau A, the river was again diverted, this time away from its natural channel and through the completed gates. An earth dam with gravel shoulders was then built on its upstream and downstream sides. The main dam, which blocks the original river channel, is 240 metres long while an adjoining wing dam is 480 metres. When the dam was completed the diversion gates were closed which, beginning in March 1982, impounded the water behind the dam up to and over a temporary weir which had been built downstream of Ōhau A. In 1984 the lake was temporarily lowered by 3 metres while this weir was removed to improve the performance of the Ohau A power station. The diversion gates now function as spillway gates to allow excess water to pass safely through the dam. The lake was officially opened on Saturday 24 April 1982. There was a weekend event which attracted 7000 spectators with the rowing course hosting a regatta attended by 188 crews and representing 80 South Island rowing clubs. Recreation The lake was developed by the Ministry of Works into a major recreational resource for the area with a large number of trees and a holiday park on the lakeside. Ruataniwha is also one of New Zealand's main rowing venues. This was not planned as part of the hydroelectric project but instead came about as facilities were constructed as a public service on the instructions of Max Smith, the locally based Project Engineer of the Upper Waitaki Power Project. The rowing course was surveyed, landscaping undertaken and anchors put down for lane markers before the lake was filled. He reached agreement with the Rowing Association that it would fund the building of the regatta control building at an estimated cost of NZ$75,000. When pressure to complete the building before the official opening of the lake raised the cost to approximately NZ$130,000 he