"That's quite funny - I couldn't believe it would be recovered ever again from the ocean," said Mr Waenga, 51, who has lived in Australia since the 1990s but was here last week for his elder sister's tangi at Potaka on East Cape.
Mr Dawson landed the key as his only catch on a long-line hook two days after it was believed lost to a watery grave.
His wife Gail noticed the name of Auckland-based Scotties 0800 Rentals on the key tag, so contacted the company to return it.
But that was too late for Mr Waenga to be spared the cost of having his Nissan Tiida rental car towed to Whakatane, sending to Auckland for a computer chip to replace the transponder, and booking a later flight home.
The lawnmowing contractor had bought a moki fish at Opotiki on his way back to Auckland, and popped into the ocean near his niece Dawn Murphy's Matata home to clean its scales - with the car key in a side pocket.
"I went in about knee deep, but was pushed backwards by a big wave," he said.
He was joined in a fruitless coastal search by Mrs Murphy and other relatives, before contacting the rental company to arrange for Nissan to replace the transponder.
"He wasn't too happy," Mrs Murphy said of her uncle's predicament.
"I said your moki ended up costing you $700 and something."
The extra cost included $598 for the replacement transponder and a towing fee, and $110 to rebook his flight.
Rental car company owner Keith Scott said replacement prices charged by vehicle suppliers ranged from $500 to $600.
"They're the biggest blimmin rort out," he said.
Mr Waenga's Australian wife Sue shared the expat Kiwi's laughter, having been softened up on his arrival home not only with the frozen moki but a crayfish he thought prudent to stock up on before leaving New Zealand.
"That's what got him off the hook," she said.
Mr Dawson was back out fishing and could not be reached for comment, but his wife hoped he would redeem himself by bringing home a tastier catch than last week's.
