The falls, which have not been open to the public for more than a decade, have been treated like a rubbish dump by some of those arriving by jumping the fence, with the landowner having to deal with 14 car loads on one recent occasion.

Owners, Anna and John Hyles, are also working on a plan to reopen the falls to the public within 12 months, but are pleading with the public to be patient.

The plea comes after a teenage boy was injured but lucky to be alive after he slipped on mossy rocks and fell 15 metres at the falls on December 20.

"We are at our wits end and are worried of the thought of teenagers out there when the infrastructure is just not at a level that I'm confident about," Mrs Hyles said.

"There is no one keeping an eye on it, and all the facilities that were part of the tourist park – the hand rails, the walking trails, etcetera – have all been dilapidated, so it is currently not safe."

She said the attitudes of trespassers when told to leave was often appalling, with some threatening to "burn down the paddocks" of landowners, then leaving beer bottles and litter behind.

The land was initially run as a tourist park after Mr Hyles' purchased it in 1983. The family closed the park in 2004 due to insurance issues.

However, it could be reopened to the public by December 2016 once the peninsula is redesigned.

The Riverview Group is proposing 11,500 homes in a continuous community straddling the border and bounded by the Murrumbidgee River and Ginninderra Creek.

The proponents propose a conservation trust, drawing on multimillion-dollar contributions from the ACT Government and NSW land sales, to manage the river corridor. Mrs Hyles stressed that she wants locals to enjoy "the absolute jewel in the crown of Canberra", but not while it is dangerous and illegal to do so.

"We are extremely optimistic at having something ready [for it to open] next year," she said.

But Ginninderra Catchment Group waterwatch co-ordinator, Damon Cusack, said there are a number of issues to be worked through before it reopens, such as protecting Indigenous heritage sites.

He also warned that the dangerous areas where people are getting hurt would likely remain off-limits.

"At the top of the falls, where the rocks get a little bit wet and very slippery, they are very dangerous places even when you have someone there managing the area," he said.

"I don't think any park would have them open to access; you're likely to have some very serious injuries or even die from falling from those heights."

He is calling for a higher police presence at the creek with more frequent drive-bys, and said property owners should not have to cop attitude, abuse and threats from trespassers.

Despite only being able to access the Ginninderra Falls through the ACT, it is NSW land.

Superintendent of the Hume Local Area Command, Zoran Dzevlan, said he had arranged for ACT policing to do additional patrols of the area.

"We have also spoken to ACT roads [Territory and Municipal Services], who have indicated they will put additional signage to warn people, one: that it is a no-through road, and two: the dangers associated with crossing into the land and partaking in activities on the land," he said.

There are various penalties for unlawful entry and offensive conduct in the ACT and NSW, where the land is fenced or enclosed.