Mighty River Power and the Tuwharetoa Maori Trust Board have signed a deal over water in Lake Taupo, the terms of which the electricity generator says are confidential.
The deal runs for 52 years and provides an "enduring set of arrangements" for the lake's operation.
Mighty River chief executive Fraser Whineray said the deal was confidential but did not impose any new restrictions on how his company could use water from the lake for its Waikato River hydro system.
"We're not disclosing the key commercial terms [but] an operating easement will be registered in on the Lake Taupo title," Whineray said.
He said the length of the deal extended well beyond the current resource consent, which expires in 2041. "It won't detract from any of the operating parameters for the Waikato hydro scheme."
Lake Taupo is the main source of Mighty River's hydro scheme, which accounts for about 10 per cent of the country's electricity supply. The hydro storage also benefits downstream users, including giving Hamilton and Auckland drinking water.
In the lead-up to MRP's partial listing last year there was speculation the company would have to pay for the right to store water in the lake.
Tuwharetoa were reported then as previously being happy for Mighty River Power to store water on their land free of charge when it was fully owned by the taxpayer but the sale of 49 per cent of the company had led to a change of heart.
A MRP spokeswoman said the settlement was below the threshold for a material impact on the company which would need to be disclosed to the NZX.
Tuwharetoa trust board chairman John Bishara said the agreement would be beneficial to all involved.
Tuwharetoa trust chief executive Topia Rameka said the trust outlined the agreement at its annual meeting at the weekend and it was universally supported.
Mighty River Power shares closed unchanged yesterday at $2.99.