Coal mining has “stuffed” a World Heritage-protected lake system south-west of Sydney, according to new research.

For almost 40 years, the Tahmoor Colliery has been operating near the Thirlmere Lakes.

Now, the author of a new report says that despite the colliery operating with approvals and under strict regulations, the lakes have been damaged.

“Whatever constraints we set 30 years ago have not been good enough,” research co-author Philip Pells has told the ABC.

“We have severely impacted, and I would say stuffed this national park. And we have to do something about it.

“There is a strong body of evidence now that the groundwater lost to the coal mine has impacted on the lakes.

“Instead of them filling up after significant rainfall events, they have hardly come up at all.”