As the last station on the Waikato hydro system, Karapiro is available to help manage flows in the lower river. Even at times of low inflows to the catchment and low electricity demand, the station operates to meet minimum required flows in the lower river. Transmission lines connect the station with the national grid at Hamilton, as well as supplying regional sub-stations at Hinuera and Te Awamutu.

There is a museum at the Karapiro power station where visitors can learn more about electricity generation and the history of the Waikato hydro scheme.

History

Work began on Karapiro, the Waikato hydro system's second dam, in 1940. A shortage of labour and materials during the war meant progress was slow, the dam taking seven years to build instead of the scheduled three. The shortage of materials overseas encouraged the use of New Zealand-designed and manufactured components for the project.

Adding to the difficulties, extensive boring showed it was necessary to inject tens of thousands of tonnes of concrete into the foundations to control water seepage. Faulted, jointed rock caused leakage and instability created technical difficulties that had to be overcome by innovative construction techniques.

The 700 construction workers on the scheme at the height of the project were housed on-site and had access to facilities such as a post office, recreation room and library.

Karapiro was finally completed in 1947. When raised, the lake submerged the first power station on the Waikato River, Horahora, built in 1913 by the Waihi Gold Mining Company. In 2000, work to strengthen the Karapiro dam's left abutment was completed.

How Karapiro got its name

'Kara' means stone, 'piro' means evil-smelling. According to legend, Karapiro was the stronghold of the chief O-Te-Ihingarangi, and was where the Ngati Haua and their Tauranga allies made a defensive pact during the land wars of 1864.