Todd Energy is taking a cornerstone stake in a tidal generation project in the Kaipara Harbour.
The private energy company is investing in Crest Energy, which hopes to have the $600 million up and running within the next decade.
Crest plans to attach 200 turbines to the bottom of Kaipara's main channel, which would generate 200 megawatts of power and supply about 250,000 homes.
A spokesman for Crest Energy, Anthony Hopkins, says the project won resource consent but was taken to appeal, and a verdict by the Environment Court is awaited.
The company has received a special Government grant of $1.85 million for the scheme, but this can not be spent until the project is actually being built.