Quarterly Operational Update

Quarterly Operational Update for the three months ended 30 June 2025. QUARTERLY HIGHLIGHTS > FY25 HYDRO GENERATION 3,410 GWH - 4th lowest generation from Waikato scheme since 1980. > MEAN HYDROLOGY INCREASES TO 4,140 GWH FROM FY26 - uplift from Digital River and Karāpiro rehabilitation. > KARĀPIRO HYDRO REHAB PROJECT CONCLUDING - third unit at Karāpiro anticipated to be completed in September 2025. COMMENTARY MARKET SUMMARY National hydrological inflows of 62nd percentile during the quarter contributed to lower spot electricity prices averaging $216/MWh in Auckland. Forward electricity prices have eased to $179/MWh in Auckland for financial years 2026 to 2027 as of 30th June 2025. FY25 HYDRO GENERATION THE 4TH LOWEST FROM THE WAIKATO SCHEME SINCE 1980 Total generation for FY25 was 7,906GWh (874GWh, 11% lower than PCP). This primarily reflects lower hydro generation of 3,410GWh (686GWh, 17% lower than PCP) driven by 12th percentile Waikato catchment inflows and a lower than average Lake Taupō starting level. Lower wind generation of 1,936GWh (125GWh, 6% lower than PCP) from lower wind speeds and lower geothermal generation of 2,559GWh (63GWh, 2% lower than PCP) from planned outages contributed to the lower FY25 total generation. For the quarter, a low Lake Taupō level and dry conditions to start the period contributed to lower hydro generation of 864GWh (155GWh, 15% lower than PCP). High hydro inflows at the end of the quarter increased Waikato catchment inflows to 79th percentile for the period, providing a healthy hydro storage leading into FY26. INCREASING MEAN HYDRO GENERATION FROM DIGITAL RIVER AND KARĀPIRO REHABILITATION Looking ahead, Mercury’s average annual hydro generation has increased 62GWh to 4,140GWh per annum. The uplift in the mean hydro expectations is driven by the Karāpiro Rehabilitation Project and the Digital River, Mercury’s AI-powered decision platform and digital twin. The Digital River optimises hydro operations by simulating complex hydrology scenarios for value and has already contributed to record high hydro efficiency in FY25. KARĀPIRO PROJECT CONCLUDING WITH THIRD UNIT Mercury is anticipating the completion of the full replacement of the third generating unit at Karāpiro hydro station in Sep-25, concluding the three-year programme of work at the site. The full replacement of the three units at Karāpiro increases hydro capacity by 16.5MW, resulting in 32GWh of additional generation assuming average inflows. [For Operational Statistics and Charts, please refer to the attached] ENDS Howard Thomas General Counsel and Company Secretary Mercury NZ Limited For investor relations queries, please contact: Paul Ruediger Head of Business Performance & Investor Relations 027 517 3470 investor@mercury.co.nz For media queries, please contact: Shannon Goldstone Reputation and Social Impact Lead 027 210 5337 mercurycommunications@mercury.co.nz