Waikato-Tainui is appealing a decision allowing Auckland to take 300 million litres of water from the Waikato River every year.
The decision from a board of inquiry appointed by the Minister for the Environment effectively doubles Auckland's water allocation from 150 million litres, for the next 20 years.
Waikato-Tainui chair Linda Te Aho says Tainui is concerned the larger take will detrimentally affect the river and those who live on it.
"We remain concerned with the undermining effect on te mana o te awa and the mana whakahaere of Waikato-Tainui and our hapū and marae along the river.”
Te Aho says while she will speak to Watercare and government representatives, her responsibility is to the awa and people of Tainui.
"It is absolutely clear to us is that our tupuna river should not be used to fix decades of failed infrastructure investment," she said.