For more than 30 years, Keith Muir has campaigned to save the environment through the Colong Foundation for Wilderness.
He played a crucial role in getting the Greater Blue Mountains registered as a World Heritage Area.
Now the new Mountains resident finds his own environment at risk from a massive development which he fears could sweep away his yard.
Mr Muir bought his Carlton Road property in Katoomba in July, moving from Sydney to his own patch of retirement paradise featuring endangered swamps and a creek, which is a tributary of the Kedumba River,
He knew there had been a development application (DA) for a 26-lot subdivision on the large landholding in Stuarts Road uphill from his home, but also learnt it had been knocked back in 2020 by a local planning panel.
Mr Muir thought that if the owners put in a new DA, he would have the opportunity to raise his concerns about the impact of heavy runoff on his home.
But he was not aware that there was an earlier DA for a 46-lot subdivision, knocked back by council in 2013 but later upheld by the Land and Environment Court, giving the go-ahead for 43 new residences.
After the 2020 refusal, the owners were entitled to rely on the old DA and work has now started on the site.
Mr Muir's great concern is that, despite a stormwater management plan for the new development, in heavy rain water will still cascade down the hill and further erode the creek which runs through his property.
Removing bush, which absorbs water, and replacing it with hard surfaces, including a new road, kerb and guttering, leave him feeling vulnerable.
"I'm anxious because I'm on the creek that's downstream," he said. "It flows through my property ... and the creek is eroding upstream and collapsing already."
With the addition of bitumen or concrete in the new development, he fears his yard could be washed away. He is also worried about the survival of the hanging swamp
Two Ward 1 candidates have expressed their concerns, too. Sarah Redshaw (Greens) said: "There has been significant erosion of the waterway and drying out of the native swamp with the water level dropping. Further impact is likely from continued clearing of land higher up. Significant work is required to mitigate damage that has already occurred and to reduce the impact of further development."
And Suzie Van Opdorp (ALP) said several residents had been in touch with her and she was planning a Zoom meeting with them this week.
The development's project manager did not respond to a request for comment.