OK Tedi Mining officially suspended operations on Wednesday, with management blaming continuing dry weather in Papua New Guinea's Western Province.
The mine, which is dependent on the Fly river for the shipment of its copper concentrate out and bringing in of fuel and supplies, can no longer operate as river levels continue to drop.
The company says most OK Tedi workers are being stood down but they will receive a basic allowance.
Schools and other facilities operated by OK Tedi are being shut down with workers from other provinces being repatriated to their home provinces.
The company says the duration of the shut down is uncertain and says it will be monitoring the situation to determine an appropriate time to resume operations.