The Vale nickel company in New Caledonia says it has restarted its plant after last November's effluent pipe breakage.
The six-billion US dollar plant halted operations after it became known that the pipe leading through a lagoon of a World Heritage site was broken.
The company says the 26-kilometre pipe has been repaired and reconnected with the approval of the authorities.
Vale says the incident caused no damage to the environment but there was criticism that the authorities and the mining giant have been too lax.
Five years ago, Vale caused an acid spill and was fined, but the sentence has been appealed by the prosecution, with a ruling due next month.