"Are you all right, mate?" the worker asked, according to a council investigation report.
"No, help me. I think I've broken my back," Mr Keys replied.
The park's owner, the Hauraki District Council, cordoned off the sinkhole and began an inquiry.
Mr Keys, meanwhile, spent months at South Auckland's Otara Spinal Unit coming to terms with the fact that he would never again walk, or pursue his passion of hunting.
He is now back at his Waihi home where carers provide round-the-clock support.
But at least he is reunited with his beloved Bailey, which his family say is critical for his wellbeing. "That means a lot to him. They keep each other company and I think it goes both ways," eldest brother Ian Keys said yesterday.
"Dave is a quadriplegic and he always will be. Nothing ever changes once you are like that. But at least he can talk, which is a blessing."
The Keys family were unhappy with the council's serious harm investigation report, which claimed a contributing factor to the accident was that Mr Keys was riding without lights, and off the path.
They considered mounting legal action against the local authority but Mr Keys said they chose not to pursue it.
"District councils have quite an immunity against any form of prosecution. There's nothing you can really do about it," he said.
Two-year-old hunting dog Bailey stayed with David Keys after he fell into a sinkhole. Photo / NZME.
Now, he hopes the council and other local authorities nationwide will have learned lessons from what he called a "totally avoidable" tragedy.
WorkSafe NZ said the mishap fell outside its jurisdiction.
The council's investigation failed to pinpoint how long the sinkhole, or tomo, had been there. It found the area had "very soft underlying un-engineered fill material" of rubbish and plant matter to a depth of 4.5m, creating mini voids between 1.5m and 3m below the surface.
A council spokesman yesterday said the site had since been "remediated".
The council report made three recommendations to improve best practice, including routine checks of high-risk sinkhole areas, signage advising cyclists to stay on sealed areas in parks or domains, and a review of its hazard alert practice.
The council also commissioned an independent report by Napier-based George Spiers Consultants. It suggested the council implement a hazards register and appoint a serious incident manager.
The independent report also slammed the council's standard operating procedures for its parks and reserves staff as being "outdated" and requiring "a major overhaul".
