The Environment Protection Authority's (EPA) environment regulation group deputy chief executive, Greg Sullivan, said the organisation was investigating three discharges of water contaminated with heavy metals from the Straits Hillgrove goldmine into Bakers Creek.

The incidents occurred in August, September and October.

"Continued wet weather and a build-up of water in the Straits stormwater storage and recycling system dam has resulted in three overflows of contaminated water from the mine into Bakers Creek," Mr Sullivan said.

"The mine site is situated on a very steep hill side and the dam collects rainfall from the processing area, office buildings and car park.

"It is estimated that a total volume of approximately 0.9ML of contaminated water may have entered the creek from the overflows since August.

"However, monitoring data demonstrates that the overflows have been significantly diluted and the downstream water quality has not been impacted."

An EPA spokesperson said because of the dilution there were no environmental impacts. NSW Health has informed downstream water users as a precaution.

Straits has since had to operate evaporators to reduce the water in the stormwater system.

Four are now in operation, with another larger evaporator to be installed by the end of the month.

The company was also required to take water samples and monitor discharges into the river after each flow.

"The EPA will monitor progress of the implementation of these measures and will take action if they are not implemented to a satisfactory level," Mr Sullivan said.

Straits will voluntarily conduct tests to investigate the potential treatment of stormwater in the dams to remove contaminants, and will look at reducing the catchment area and isolating run-off.