Western Australia's Environment Minister has been unable to confirm whether it is safe to swim or fish in Cockburn Sound due to potential contamination from toxic firefighting chemicals used on the HMAS Stirling naval base.

In response to questions about the safety of the sound, Albert Jacob referred the ABC to an environmental monitoring report published in September 2016 which showed the waters were suitable for recreational activity.

But this report could not have taken into account the impact of potential contamination by the chemicals contained in firefighting foam used on HMAS Stirling until 2004.

That is because Mr Jacob's Department of Environment Regulation (DER) was not alerted by the Department of Defence to high levels of contamination at HMAS Stirling on Garden Island until October 21 of this year.

Defence has recently begun an extensive environmental investigation into contamination, looking at whether contaminated water could have leached into Cockburn Sound.

Defence is investigating whether contaminated groundwater reached Cockburn Sound. ( Supplied: Department of Defence )

In response, the DER began testing for the chemicals in December.

Cockburn Sound Management Council chair Kateryna Long said the monitoring program would test water at 18 sites throughout the sound until March.

Dr Longley said Mr Jacob would need to be advised before the results of the testing were released.

But Mr Jacob would not commit to publicly releasing the results of water testing this summer, a time when many West Australians like to swim, fish and boat at Cockburn Sound.

It is also just months before the March state election.

"It is too early to determine when these results will be released. This will depend on the analysis of the data," Mr Jacob said.