Iwi should be more involved in the management and allocation of fresh water, says Maori Affairs Minister Pita Sharples.

He has also come out against trading water consents.

In a speech to the Indigenous Legal Water Forum in Wellington on Sunday, Dr Sharples said local hapu and iwi needed to be full participants in decisions on water management in their areas, and water ownership issues needed national attention.

He said Maori believed water had a spiritual significance and they had a guardianship role to play.

"We seek to maintain our collective responsibilities to respect and protect the environment and communities that give us our identity, our rangatiratanga, our mana."

The state of fresh water was not just an environmental issue but related to the Treaty of Waitangi yet Maori had not been given an adequate role.

"There remains a lot of uncertainty regarding the nature and extent of Maori rights and interests in fresh water and how these rights might be better reflected in New Zealand law," he said.

Dr Sharples did not support amending the Resource Management Act to better facilitate the trading of water consents (or excess water) as a way to manage availability issues.

"Not only does this set up quasi-private schemes where big business is able to buy up consents and control access to water, but allocating consents to maximise land-based activity inevitably leads to greater water quality issues," he said.

"This narrow focus on economics is driving the degradation of natural water sources by pollution, abstraction for irrigation or power generation, and the flooding and droughts made worse by deforestation and climate change."