The Guardians of the Manapouri and Te Anau lakes warn that the lakes will be put at risk if plans to partially-sell State energy companies proceed.
Spokesperson Alan Mark told Parliament's Finance and Expenditure Select Committee on Wednesday that a partially privatised company operating under the Companies Act is likely to operate in a different way.
He said they might not view the conservation value of the lakes in the same way as Meridian Energy.
Mr Mark said the Guardians have had a good relationship with Meridian to ensure the conservation values of the lakes are safeguarded.
