In early 1946, the Minister of Public Works Bob Semple, announced a full development of the Waikato River, with the first three stations planned at Ohakuri, Whakamaru, and Maraetai.

Because of the narrowness of the gorge, the powerhouse took up the entire length of the base of the dam, meaning no orthodox spillway could be constructed.

Problems were encountered right from the beginning - the Second World War had just ended, which meant there was a great deal of shortages of labour and materials.

The Public Works department's work-force was less than two-thirds of its pre-war size, with thousands of vacancies not filled.

However, work was slowed by large amounts of water that poured into the tunnel until it was extensively grouted with cement and bitumen and lined with concrete.

Work then started by building cofferdams to block the natural channel of the river and allow dam construction to begin.

The Taupō control gates were shut to lower the water level in the Waikato, and 11 bulldozers frantically pushed spoil into the river to stop the natural flow.

Eventually, contracts were let to Canada for the generators and the United States for the turbines, both being more experienced and the price being 40% less than the British equivalent.

On 31 October 1952, Maraetai generated its first electricity, producing 30 megawatts (40,000 hp)on a reduced load and half head.

The reduced head was maintained while the diversion tunnel was stopped with a huge 30-metre (98 ft) long concrete plug.

The head was raised to 175 feet (53 m) in April 1953, and the station was officially opened on 5 September 1953 - two years after the target completion date.

In 1961, work on Maraetai II was suspended when the newly elected National government, led by Sir Keith Holyoake, shifted priority to building the HVDC Inter-Island ("Cook Strait cable") between the North and South Islands, following a significant increase in electricity demand.

With the inter-island link completed in 1965, work recommenced on Maraetai II, with the first two turbines and generators were finally commissioned in July 1970.

The last turbine and generator, and the last on the Waikato River, being commissioned in February 1971 - almost 25 years after construction of Maraetai began.

From Whakamaru, electricity generated at Maraetai is distributed via Transpower's 220 kV grid to Hamilton, Taupō, Palmerston North, and Auckland.