The Waitangi Tribunal has heard that pipi beds in Whangaroa harbour were deliberately poisoned to make way for oyster farming.
The Tribunal has been hearing evidence in Kerikeri this week in its Ngapuhi inquiry.
Kuia Ani Taniwha said the commercial farming of Pacific oysters had edged out the native oyster prized by local iwi.
She said the pipi beds in the harbour were intentionally destroyed.
Mrs Taniwha said one morning in the 1970s the residents of Whangaroa awoke to see a green foam floating on the harbour.
She said after enquiring to local authorities they were told that detergent and diesel was poured on to the pipi beds to kill them to make room for Pacific oysters.
Mrs Taniwha said Whangaroa hapu had been stripped of their right to exercise kaitiakitanga over the harbour.