Irrigation New Zealand says a proposal to expand irrigation water supply for the Canterbury Plains must not disadvantage water users further downstream.
TrustPower plans to develop its Lake Coleridge site to expand its hydro-energy production and increase the water available for irrigation.
Lake Coleridge would be used to store water from the Rakaia River when flows are high, with the water being used to irrigate up to 60,000 hectares more land in the summer.
For that to happen, a water conservation order on the river has to be changed and more than 200 submissions will be heard over the next six weeks.
In its submission, Irrigation New Zealand says several downstream farmers are concerned their water takes will be reduced if the project gets the nod.
TrustPower commercial operations manager Chris O'Hara says it's looking into those concerns.
He says, at this stage, it is not clear under what circumstances the farmers would be unable to take water where, historically, they would have been able to in the past.
Mr O'Hara says TrustPower will work with them to undertake the technical hydrological work needed to determine exactly what the position is.
He says the two sides then need to agree what the affect is, if any, and if necessary put in place appropriate mitigation.