Why a Queenstown pack rafter got into difficulty in a gorge on the Caples River in 2021 can’t be fully explained, a coroner says.

Department of Conservation researcher Stephen Bowler, 30, drowned on November 22 during a three-day trip in the Greenstone and Caples valleys, near Lake Whakatipu.

In her findings, coroner Heather McKenzie says he was an experienced tramper and pack rafter who’d been on the river earlier that year.

After spending the previous two nights at the Greenstone and McKellar Huts, Bowler and friends Matt Ward and Mary Mitchell began rafting the Caples River about noon.

About 1.30pm, Bowler was in the front raft when he entered a gorge about 1.5km upstream of the Mid Caples Hut.

His friends got out of the river before the 350m-long gorge to walk around it, having earlier determined they wouldn’t try to raft it.

Mitchell described Bowler as making a ‘‘clear forward paddle stroke and was clearly not trying to get away from the gorge’’.

Ward looked down from the river bank a few minutes later to see a jacket in the water.

He ran around the gorge and back upstream to see Bowler lying face down in the water against a rocky bank.

As he waded towards him, he pushed aside his water-filled raft.

By that point, Ward estimated his friend had been face down in the water for up to 10 minutes.

Ward and Mitchell pulled Bowler to an island and set off a personal locator beacon — a chopper and police arrived at the scene, but Bowler couldn’t be revived.

Bowler had experienced issues with water getting into his raft earlier in the day because he didn’t have a spray skirt.

Pack rafting guide Huw Miles told police he didn’t think that was an issue because Bowler got into difficulty near the beginning of the gorge, before his raft had filled with water.

A pathologist concluded Bowler drowned after becoming unconscious as a result of arrhythmia — an irregular heartbeat — caused by a congenital heart defect.

That could have been triggered by an increase in blood pressure caused by the stress of entering a dangerous stretch of river.

But McKenzie couldn’t make a specific finding about why Bowler got into difficulty.

His equipment was ‘‘generally fit for purpose’’, but he might have been rafting beyond his experience and ability.

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