Hydro generation

HYDRO.

We harness the power of water through our nine hydro plants along the Waikato River to produce about 10% of New Zealand’s electricity. The great thing about hydro generation is that it can be increased or decreased quickly to meet peak demand for electricity. Our hydro system is the largest peaker in the North Island – and located close to the country’s largest city Auckland.
Find out about the Mercury Taupō Community Fund.

HYDRO STATIONS

ARAPUNI

Protected under the Historic Places Trust Arapuni has the largest capacity of any station in the Waikato hydro system.

ARATIATIA

13km downstream from Taupō, Aratiatia is the smallest hydro reservoir in the Waikato Hydro System

Ātiamuri

Originally designed for three generators, a fourth was later added and commissioned in 1962.

KARāPIRO

188km downstream of Lake Taupō, the Karāpiro Lake is the home of NZ Rowing.

MARAETAI I AND II

Combined, Maraetai I and II offer the largest output from any lake on the Waikato River.

ōhākurī

Lake Ōhākurī covers 12 sq km and is the largest lake on the Waikato River.

WAIPāPa

The smallest power station on the Waikato River and is used to supplement other stations.

WHAKAMARU

The main switching station for upper Waikato generation and supplies the transmission system that leads north

UPGRADING OUR VITAL HYDRO ASSETS

Our hydro stations on the Waikato River were constructed from the late 1920s to the 1970s and have worked hard to keep the country powered. We have a long-term hydro refurbishment programme to protect these assets to ensure they can manage water flow that looks after the environment but also can optimise energy from the awa.

In 2019 we begun a ~$90 million upgrade of the Karāpiro Hydro Station. This project replaced all three of the turbines, increasing the installed capacity to 112.5MW and was completed in September 2025.

Main works for the Dam Enhancement Project at Arapuni Dam are planned to commence in April 2026 and expected to take 24-36months.

The following upgrades are scheduled:
2029-2032 Generators and governors at Ōhākurī will be upgraded to increase annual generation by 10GWh.
2030-2034 Turbines, generators and governors at Maraetai I will be replaced to increase annual generation by 45GWh.
2031-2034 Turbines and generators at Ātiamuri will be replaced to increase annual generation by 32GWh.