They were fishing at a spot popular among anglers, known as the Magic Carpet.
"I felt a wee hit on my rod... I thought it was a snag and my mate who was with me thought it was a snag, but then it started running."
That was when he realised he had hooked a fish, though initially, it did not put up much of a fight.
"It felt like a 10lb trout really. Then it started picking up its strength and then it started really going.
"Adrenaline was pumping through me. Everything was happening all at once. I had a glimpse of it when it came to the surface and I was like 'holy, this is a big trout'."
His friend was able to get the trout in a net.
The rainbow trout would live to fight another day as Byron decided to release it.
"I do it for the passion. I like being outdoors and I like seeing how the trout fight in the water and how they survive and how they get all their food. Us anglers, we have to try to match what they're eating. It's a bit of a competition to try to catch these big trout, or any trout really."
While there was no obvious record of a bigger rainbow trout being caught in New Zealand, Fish and Game central South Island ranger Rhys Adams said it was likely bigger ones had been caught in the past.
"[But] it's still a bigger trout than 99.9 per cent of trout anglers will catch in their lifetime," Adams said.