Parts of Glenbrook Native Plant Reserve are being eaten away by creek erosion, killing native plants in the water's path.
The four-hectare reserve is maintained by a small band of volunteers, and is run by a committee headed by Dick Turner.
Knapsack Creek runs through the reserve, and Mr Turner believes increased run-off water generated from development upstream, was creating erosion, as water-slowing measures were ineffective.
"We have got erosion in the creek that wasn't there five years ago," Mr Turner said.
Blue Mountains Council land borders part of the reserve, where sandstone blocks were deposited in a tributary of Knapsack Creek in 2016 to slow the water rushing into the reserve. This effectively slowed the water on the council land, but has gouged a half-metre deep hole at the reserve and wiped out native plants across 10 metres of bushland.
At the August council meeting, councillors agreed council staff would look at the problem area, carry out work on neighbouring council land if required, and work with the volunteers to help them obtain grants for remediation works.
A Blue Mountains Council spokeswoman said that council had applied for a federal government grant of more than $19,000 under the Communities Environment Program, and expected to hear in November if the application was successful.
"If successful, council has offered to manage the project," the spokeswoman said.
"In addition, council staff are meeting with Water NSW / Sydney Water representatives regarding the potential to apply for upstream-funded works as soon as possible."
Mr Turner was hopeful the grant application would be successful.
"I'm hoping repair work, creek work, will slow the erosion here and there," Mr Turner said.
"I hope that we will get this grant and work will proceed."
He said all the undergrowth plants, such as native violets, had disappeared as a result of the erosion.
"While there's bare earth, there's no native plants," Mr Turner said.
"It will end up with more sand and silt in the Hawkesbury River, which they don't want."