THE Greens have called on the NSW Government to rule out the sale of Essential Energy's Nymboida hydro-electric power station or ensure its water rights remain in public hands.

Greens MP John Kaye said the future of the station, south-west of Grafton, had been kept secret from voters.

"While the NSW Coalition has granted Essential Energy a temporary exemption from the planned poles-and-wires sell-off, the future of the state-owned corporation's generating assets is less than clear," he said.

"The community has good reason to be concerned that the power station and the associated water rights are being scoped for sale.

"Essential Energy made it clear in their last annual report that they intend to exit from the business of generation to focus solely on electricity and water distribution."

Mr Kaye argued any water rights should remain in public hands.

"If it is to be sold, the water rights must be detached from the owners and returned to the community."