Defending champion Kane Radford has more at stake than national titles in the New Zealand Open Water Swimming Championships in Taupo at the weekend.

Radford, along with the leading New Zealand open water swimmers, has eyes firmly fixed on the FINA World Championships in Russia in July.

Rotorua open water swimmer Kane Radford. Photo: Supplied.

The national championship, which are part of the Epic Swim event, is the first stepping stone in that process, with swimmers needing to finish in the top five in the 10km men's and women's events on Saturday.

Successful swimmers then move on to the BHP Billiton Aquatic Super Series in Perth on February 1 where they will need to finish in the top six (of Australian and New Zealand swimmers) to automatically secure qualification for the world championships.

Australian-based Radford will be chasing his fourth straight national men's title in the 10km event - building on a strong 2014 year which saw him win the bronze medal at the Pan Pacific Championship.

The 24-year-old, originally from Rotorua, will be looking to stamp his class on the field, with an all-Kiwi line-up as the leading Australians are preparing for the BHP Billiton event which doubles as the Australian championships.

His major challenges will be expected from the 2011 national champion Phillip Ryan (Waterhole), Waikato's Troy Balvert (St Peters), who tested himself on the World Cup circuit last year, and Wellington's Liam Albery, who was fourth in the junior Pan Pacific Championship in Hawaii.

Defending women's champion Charlotte Webby, 26, is the hot favourite to claim the national honours in the women, with last year's leading Kiwi, Grace Somerville missing this year.

The Taranaki swimmer took the official national title with Somerville racing in the junior division, and went on to finish an encouraging sixth place at the Pan Pacific Championship in a strong field led by Olympic medallist Haley Anderson (USA).

Webby will be challenged by Penelope Hayes (St Peters) and Bridget Maher (West Auckland Aquatics) amid a small field.

That's not the case for the bumper entries in the recreational swims that form part of the sixth Epic Swim event which has attracted a record 850 entries, which has nearly trebled since the first event in Taupo in 2010.

The 10km New Zealand Championship is on this morning along with a range of recreational swims from 100m to 10km, with the 5km national championship and a masters race on Sunday.