The smelter had reduced its power use over the past few months as the country felt a squeeze on its power supplies.
The owner of the smelter, NZ Aluminium Smelter, had come to an agreement with its power suppliers to reduce consumption by more than 200MW.
It initially had reduced it by a total of 185MW which had led to a downscaling of the smelter.
An additional 20MW was then made available by the smelter to the national grid in late August to help with the power supply.
Lake levels in the South Island hydro system were at record lows for the time of year and there was a risk of not having enough water storage coming into the summer.
But a very wet September had led to lakes rising significantly.
The level of New Zealand’s largest hydro storage lake — Lake Pukaki — was above the 91-year average for the first time since May, Meridian Energy said on Tuesday.
Lake Hāwea, which feeds the Roxburgh and Clyde power stations on the Clutha River, has had a storage increase of 78% in the past four weeks, rising about 2m.
It is now back to average storage.
Lake Manapouri, which feeds the Manapouri power station, was sitting at 179.23m, slightly above its maximum operating range.
When contacted, an NZ Aluminium Smelter spokesman said the smelter had now started to ramp up, which would see the potline fully operational by April next year.
No workers were stood down during the drop in power usage.
The ability to offset power was part of a new energy agreement signed in May this year which allowed power companies to decrease supply to the smelter in times of national power shortages.
