Restrictions have been placed on water takes from the Opuha Dam in South Canterbury because of a lack of winter snowfall.
The dam supplies the Timaru community and farmers for irrigation and produces electricity.
It has only had restrictions applied twice before in its 12-year existence, both after dry summers.
The advisory group which manages the water supply says the lack of water at this time of year is concerning.
Its chair Judy Blakemore says the restrictions will remain in place for a fortnight and may be extended.
"This year we didn't get the snow and we haven't had much rain so the lake has started dropping where normally we would expect it to be rising from about now until about Christmas.
"Farmers are being asked to take 25% less than their normal take and the (Timaru District) council's being asked to take a 12.5% reduction."
Ms Blakemore says the Opuha advisory group made the recommendation to the Canterbury Regional Council, which imposed the water take restrictions immediately.