"What was I thinking of? Well, I was convinced the track was nearby and walking back would have been easier than swimming. So I took a bearing off the setting sun and the rising moon and headed north, back the way I'd come. Or so I thought."
After an uncomfortable night on the shores of another waterfall, Mr Keys found himself completely lost.
There was no sign of tracks or access.
He details the "brainwave" he had to write a message in the sand, including the date as well as a plea for help, in an attempt to get rescued by helicopters.
"Around lunchtime I came to a sandbank and was in the process of swimming past it when I had a brainwave. It seemed a good idea to help myself as much as possible so I got out of the water, found a stick and wrote a message in the sand, just in case the helicopter came down that way. HELP. 2807."
And it was a smart move.
He was rescued a day later - after two days of helicopters scouring the area - and describes the moment of joy on his blog.
"Suddenly I heard a helicopter coming down river. I leapt off the bank into the creek but by the time I'd done so it had gone. I stood in midstream, yelling at the pilot to come back - and he did.
"He came around again while I continued to jump up and down like a lunatic and this time someone waved to me out of the window. My ordeal was over."
Search and rescue co-ordinator Senior Constable Brad Foat told Stuff.co.nz the search had been his most challenging to date.
The look on the man's face when he was found was memorable, Mr Foat said.
"I was about to enjoy a day off with my family when I was recalled to duty at 8.30am for a missing tourist," he told Fairfax.
"The details were very sketchy given that the man was a lone traveller having only befriended nearby campers just days earlier.
"The only information I had was the man's first name and that he had an English accent."
