Plans for thousands of new homes in west Belconnen could lead to the Ginninderra Falls being reopened.
The residential joint venture between the ACT government and local developer Riverview Group includes a proposal for a cross-border conservation area encompassing the falls' site.
The land's owners have asked the NSW government to consider buying part of their acreage to manage the waterfall area as a state asset.
The spectacular Ginninderra Falls, within three kilometres of Belconnen, was a popular recreation spot for Canberrans until landowners John and Anna Hyles ended access to the site in 2004 because of insurance issues.
Momentum has been building in the past couple of years for the site to be reopened as part of a cross-border national park.
ACT Economic Development Minister Andrew Barr recently announced the government would enter into a joint agreement with Riverview Group for 4500 houses next to Holt and west Macgregor in the next decade. The plans include a conservation area of about 326 hectares encompassing the Murrumbidgee River corridor on the ACT side of the border.
Riverview Group director David Maxwell said he planned to extend the protected area on to the company's land in NSW, then have the zone cover the falls.
Mr Maxwell wants to incorporate a riparian corridor from the Ginninderra Falls back along the creek to the ACT border to create a protected river link to Mulligan's Flat nature reserve.
He said the projected conservation area of almost 600 hectares would require a percentage of acreage from four NSW landowners, and a stretch of ACT land surrounding the lower Molonglo water quality control centre.
Mr Maxwell said that while it would not happen for at least a decade while the houses in west Belconnen were built, he wanted to be able to reopen the falls to Canberrans. "What we're saying is [that] on the scientific evidence we have this is the logical area to be set aside".
"From my point of view, aspirationally, if we can unlock, NSW can we also unlock that particular asset for the people of Canberra."
The conservation trust would be funded by the sale of blocks of land in the development.
Ms Hyles said the west Belconnen development proposal had intensified the need for the area to be reopened. While there had been minor problems with people jumping the fence to access the falls illegally, this would occur more often when there were thousands more residents nearby, she said.
She said it was important that the NSW government managed the site as a valuable state asset.
Advocates of a cross-border park encompassing the falls say a trust management scheme will take too long to establish.
The Ginninderra Falls Association wants a Murrumbidgee-Ginninderra Gorges national park, to be managed by rangers on either side of the ACT-NSW border.
Association president Dr Chris Watson said a trust would not work because it would take too long to raise the funds.
"It won't come for donkey's years," he said.
"It's important to try and get this established and for the ACT government to get a bit of backbone behind it."