Protesters have blockaded ACC's offices in Wellington with dairy sewage to protest a Hawke's Bay dam.

Greenpeace has put six tonnes of dairy sewage at ACC's former head office in Wellington as a protest to a controversial irrigation scheme.

About 6.45am on Wednesday, cow urine and other dairy waste, sealed in eight heavy-duty tanks, were placed across the two main entrances into ACC's offices on Molesworth St to draw attention to the Ruataniwha irrigation scheme in Hawke's Bay.

Greenpeace's agriculture campaigner Genevieve Toop said ACC could potentially waste millions of dollars on the dam, which opponents say will pollute nearby waterways.

TOM HUNT/FAIRFAX NZ Greenpeace protesters at ACC's head office in Wellington.

ACC has been tipped as a potential investor in the $330 million scheme, although the corporation has refused to confirm whether it is in negotiations to invest.

In a statement, Topp said: "So we've blockaded ACC's offices in Wellington today with six tonnes of dairy sewage, including cow piss, in large, sealed containers. Millions of tonnes of pollution ends up in our rivers via cow piss already. And this pollution will only get worse if government departments like ACC throw taxpayers' money at irrigation schemes like Ruataniwha that expand the industrial dairy sector."

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A computer-generated image of the Ruataniwha Dam in central Hawke's Bay.

Supporters of the dam scheme believe it will give a massive boost to farms in the region.

The tanks that the waste is in are intermediate bulk containers, which are specifically designed for transporting and storing large amounts of liquids.

ACC's head office in Wellington is now part of the Justice Ministry building, although some ACC staff do work at the old building.

A spokeswoman for the corporation said: "ACC has a policy of not commenting on things we may or may not invest in. We respect the right of Greenpeace to protest peacefully".

In a statement, Federated Farmers called the protest "misguided".

"It's disappointing to see Greenpeace opposing a scheme that has gone through a lengthy process and has stringent environmental conditions attached to it," Federated Farmers water spokesperson Chris Allen said.

"Greenpeace are demonstrating their anti-irrigation views and seem to oppose anything that gives New Zealand farmers climate resilience."

ACC had not been confirmed as an investor for the scheme, he said.

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