The Australian based miner, St Barbara, has issued a warning to communities living around its Gold Ridge mine in Solomon Islands, saying the tailings dam could overflow.
The mine has been shut since April after extensive flooding on Guadalcanal.
The company says the water in the storage facility is already too high and it wants to ensure there is no unpredictable overflow.
It says despite months of requests and negotiations, the Solomon Islands government has not yet given approval for a controlled discharge.
The company says the water treatment plant at the dam was destroyed by vandals for the second time in August so the only way to lower the water level in time to stop an overflow is to discharge untreated water.
It says recent independent tests show that the water it intends to discharge meets international aquaculture safety guidelines and is safe to release into the Tinahulu River without treatment.