The Green Party is calling for the Government to come clean on what it describes as secret discussions with Trustpower, to weaken a water conservation order for the Rakaia River.
Conservation orders can be used to preserve the natural state and characteristics of waterways and can restrict taking and discharging water.
Trustpower has confirmed it's looking a number of scenarios for increasing its hydroelectric power generation at Lake Coleridge, north of the Rakaia River, as well as the potential for irrigation projects based on the lake.
It says it's held discussions with the Government. Although no proposal has been put forward, the company says the conservation order may need to be amended for the plans to go ahead.
But Green Party co-leader Russel Norman says removing or changing conservation orders is similar to felling trees in a national park. He says the orders are fundamental for protection of the industry.
In a written response to the party, Agriculture Minister David Carter says he sees water conservation orders as having a number of disadvantages, costs and limitations.
He says he expects a newly-formed Land & Water Forum, which is charged with finding a national approach to the management of fresh water resource, to look at all areas of water management seriously.