By 11:20 am on 23 July 1956, the lake had filled to the crest of the spillway water. With a desperate shortage of electricity affecting the South Island, commissioning of the generating unit 1 immediately commenced. Once the engineers were satisfied that the machine was fit for service, it was connected at 6 pm to the national grid. Due to the reduced head, the machine's output was limited to 30 MW. By the end of the next day generating unit 2 had completed commissioning and was also connected to the system. This allowed the 220 kV line to Islington to be brought into service as two machines were needed to provide sufficient reactive power to charge the long length of line. The third generating unit was commissioned on 18 August 1956 and the fourth unit on 11 December 1956. The power station was officially opened on 3 November 1956 by Stanley Goosman in the presence of 600 invited guests, plus members of the public.