Neighbours of the Tarawera River hold little hope that pollution from the largest paper mill in the country will cease after the regional council extended its resource consent.

Environment Bay of Plenty has given permission for the Tasman Pulp and Paper Mill in Kawerau to continue discharging effluent into the river, as well as gas and dust emissions, for another 25 years.

Owners Carter Holt Harvey and Norske Skog had applied for a 35-year consent.

The hearings commissioners said the permit renewal was granted under exceptional circumstances, and because there was no scientific evidence of poisoning of aquatic life.

The commissioners acknowledged the degradation of the river as a result of the discharges, but said this was outweighed by the social and economic benefits the mill provided in the forestry industry.

Green Party spokesman Gordon Jackman said the granting of exceptional circumstances for another 25 years was "laughable".

"It has been given exceptional circumstances since 1955. The decision gives them no incentive to look at improving its waste processes."

He said submitters would never afford the resources to prove the harm the mill caused.

"Unless you show dead bodies or dead animals ... the council is going to be permissive and not precautionary."

Commissioners said the companies should keep technological advances "in front of mind" and reduce discoloration of the river "to a point of inconspicuousness".

Opponents of the consent say polluting of the river - dubbed the Black Drain by environmentalists - has deprived them of its food sources and is threatening the local agriculture industry.

Organic kiwifruit grower Harry Lagocki said food exporters depended on a high quality of water, and that his product would be rejected if it didn't pass international purity tests.

Tipene Marr, leader of eastern Bay of Plenty iwi Ngati Rangitihi, had argued for a 10-year consent and a genuine commitment by the companies to reduce damage to the river.

Mr Marr said he was saddened that he would not see the Tarawera River run clean again in his lifetime.

"They are now allowing them to pollute the river for 90 years.

"We can't use the river, we can't swim in it, it's no good to us anymore."

He said they "did not have a hope in China" of preventing the mill gaining its permit.

"I didn't feel optimistic at all. There are too many economic pressures, because the mill provides more than 3000 jobs in that area."

Ngati Rangitihi wanted the mill to reduce its discharge of "colour", or solid waste, by three tonnes a day each year. It emits 31 tonnes a day.

The iwi said it had lost $49 million in food resources in the past 50 years because of mill pollution.

It was making a Waitangi Tribunal claim for that amount, based on the calculation that 50 families could collect $20 of food - fish, watercress and birds - three times a day.