Mercury NZ is pressing ahead with a significant reinvestment programme in its Waikato River hydro assets, with Chief Executive Stewart Hamilton highlighting progress in the company’s FY25 results.
The $90 million rehabilitation of Karāpiro Hydro Station is in its final stages, with the third and final generation unit due for completion in September. Once finished, the project will deliver an additional 32GWh annually and extend the station’s life by another 50 years.
Hamilton confirmed that Mercury is also planning upgrades at three further stations on the Waikato River – Maraetai, Ōhakuri and Ātiamuri – representing a $550 million investment. Together, these projects are expected to increase capacity by 58MW and add 87GWh of generation each year.
The Waikato River Hydro System, developed between 1924 and 1970, remains Mercury’s backbone. It produces about 47% of the company’s electricity, supplying around 10% of New Zealand’s national demand – an average of 4,140GWh annually.
FY25 brought tough hydrological conditions, with inflows into Lake Taupō in the 12th percentile. Hydro generation fell 17% year-on-year to 3,410GWh – the fourth lowest output for the scheme since 1980. To manage these pressures, Mercury deployed optimisation tools including “Digital River,” an AI-powered digital twin of the Waikato River, to maximise output from available water.
