STATE government changes to laws protecting creek and river banks will leave the shire's waterways at greater risk of pollution, said Total Environment Centre campaigner David Burgess.
The NSW Department of Planning and Infrastructure announced the changes this month as part of initiatives to improve housing supply.
They include allowing cycleways, roads and parks along creek banks, removing the need for planted buffer areas in addition to protected corridors along waterways.
The government also announced it was seeking to remove the federal government's role in assessing developments in these areas.
Mr Burgess, who is also active in the Sutherland Shire Environment Centre, said the changes were of great concern and could threaten the health of the shire's three rivers, the Woronora, the Georges and the Hacking.
"Riparian corridors in a nutshell are what keep our waterways clean. They are vital for filtering urban run-off." Mr Burgess said.
He said roads and cycleways along waterways would cause greater urban run-off and reduce the vegetation needed to filter water entering streams and creeks.
"Roads in particular are renowned for introducing weeds," he said.
Georges River Environmental Alliance secretary Sharyn Cullis said she had not heard anything about the changes from the government.
"I'm an interested stakeholder and involved in this area and have not even heard about this. Where is the consultation?" Ms Cullis said.
"This is an appalling move. What we are actually doing is diminishing the quality of our waterways."
The changes to protection of creek banks are not the only tinkering with environmental legislation undertaken by the state government recently.
Mr Burgess said he was also concerned by proposed changes to the Native Vegetation Act, which were announced at the beginning of the month. The changes received little attention as the announcement coincided with the state government's controversial decision to allow amateur hunters to cull feral animals in some national parks.
Mr Burgess said the changes made it easier for land owners to clear areas that were revegetated by native plants.