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Breca Swimrun returns to Wanaka this Sunday for the second time, after it debuted in the town last year.
Swimrun athletes swim and run over a multiple-stage course in pairs, and wear shoes and wetsuits for the entire race.
The Wanaka event offers two distances - a full 54km and a sprint 19km - on a course starting at the Clutha River outlet and skirting part of the lake, finishing at the Edgewater Hotel. The full course takes in Stevensons Island, the Minaret Burn Track, Glendhu Bay and Ruby Island.
Event organiser Ben de Rivaz said 140 athletes had entered, down from 158 last year.
He believed the race was going to be a "blast".
"We have lots of fantastic teams, including a number of repeat entrants from last year."
"It's a tough day out - the distances are pretty cheeky - but a stunning and rewarding course."
Swimrun was developed in Sweden in 2002, and has risen in popularity in the past three to five years.
Mr de Rivaz said swimrun was "born out of the modern desire to create increasingly innovative and challenging endurance events."
Mr de Rivaz said Breca runs five races in the United Kingdom and two in New Zealand.
The inaugural Breca Bay of Islands is set to take place next month.
He believed swimrun would continue to grow in popularity in New Zealand.
"It's rapidly becoming a huge sport in Europe."
He said Wanaka offered a "huge variety of landscape and terrain, and pristine trails in all directions - perfect for swimrun."
"We're considering new locations [in New Zealand] for 2019."