Water restrictions could be imminent, the Otago Regional Council warns as the region's river levels drop.
All rivers except the Clutha were falling towards minimum flow levels, due to a lack of rain in the past month, environmental services council manager Martin King said.
The Kakanui, Shag, Taieri, Manuherikia and Pomahaka rivers are already at low levels not usually seen until late summer.
''The Manuherikia is very low, and even the Clutha is below the level we expect for this time of the year,'' Mr King said.
MetService figures show in the past 30 days, only 20mm of rain had been recorded at its site in Queenstown, 26.6mm in Oamaru, 19.8mm in Wanaka and 27.4mm in Dunedin.
The council was advising all Otago irrigators to implement conservative irrigation practices and prepare for potential water rationing.
If no substantial rain fell throughout the region soon, there might be a need for rationing to begin later in the month or early next year, he said.
So far only the Kakanui at Mill dam was on a low level irrigation restriction alert.
Otago hydrologist Dave Stewart said the lack of rain in November meant there was nothing to boost river levels and spring winds had dried the region out.
The weather was ''glorious'' but rivers were dropping to the point restrictions were needed.
''Maybe we'll get some rain this weekend. Whether it'll produce much I don't know, but it's coming from the right direction.''
While Niwa was predicting average to below-average rainfall for the summer, no-one could predict what the next few months would bring, he said.
''We've seen these sort of patterns before, then quite often in January we get rain, the rivers pick up and the strain goes away.''
December was notoriously unsettled so there was a chance rain could come later.
Niwa's spring climate report showed Dunedin was the coolest, driest and cloudiest of New Zealand's six main centres.
Dunedin's mean spring temperature of 11.5degC was 0.5degC above normal and its rainfall of 115mm was 69% below normal.
