Spills from the Pukaki and Benmore hydro lakes are under way, as Meridian Energy controls the run-off from heavy rain that has fallen in the headwaters over the past few days.
Environment Canterbury flood controller Tony Henderson said there had been more than 500mm of rain in the Waitaki and Rangitata catchments in the past four days.
"With the exception of that week-long period we had back in 2010, it's probably the most we've had over the summer in several decades. Usually, we don't have any flooding events at all during Christmas and New Year."
Henderson said the Rangitata River rose to 2000 cumecs by 6pm on Wednesday, but levels were expected to fall over the next few days.
"It's certainly unusual, ordinarily the Rangitata runs about 100 cumecs during this time of year," he said.
"It took three days to rise to 2000 cumecs, it will take another three days to drop below 100."
The rain had been a blessing for the region's farmers with the region starting to dry out.
"It's been very welcome. We've had close to 30mm," Federated Farmers South Canterbury grain and seed chairman Colin Hurst said. "It will finish off the crops nicely."
The rain in the Waitaki catchments, and low demand for electricity, has also meant that Meridian's hydro lakes are running close to full operating level.
The state-owned generator began spilling water from Lake Pukaki on Wednesday night, and expected to continue doing so for a few days.
"As the demand for electricity will be low over this time of year, I expect Meridian will be keeping a watching brief on the situation," Henderson said.
Meridian also began spilling from Lake Benmore yesterday morning, with 800 cumecs going into the system, more than twice the usual rate.
Spokeswoman Michelle Brooker said it might need to eventually spill water from Lake Ohau if levels remained over-capacity.
Henderson said people camping in the Waitaki catchments needed to be careful about rising water levels.
"We just want people to be careful . . . If you're camping in the low-lying areas, move to higher ground."
- The Timaru Herald