'I'm probably pleased not to be swimming'

The cancellation of the swim in today's half Ironman in Taupō due to toxic algae in the lake hasn't stopped hundreds of athletes taking part.

A potentially toxic algal bloom found in Lake Taupō on Thursday led to race organisers cancelling the swim leg as a precaution.

Early this morning, hundreds of athletes showed up to complete the altered course.

Patrick Dunn did the Ironman last year, and said the change in the race didn't bother him too much, and he'd still enjoy it.

He said not having to swim made things easier.

"Swimming's my weakness so I suppose that's an advantage for me ... because it's not going to affect the time cut-offs, actually it's a bonus for me."

Mr Dunn said given the health risk it was best to cancel the swim.

Robert Macfarlane from Cairns said he was still looking forward to the day.

"This morning's probably going to be pretty cold in the lake so now in hindsight I'm probably pleased not to be swimming in the lake but certainly you haven't sort of fulfilled that whole Ironman experience ... so it's a bit disappointing."

Mr Macfarlane said he understood why organisers called the swim off.

Elaina Reibe, from Chinchilla, Australia, had been training for the event for eight months, and when she began she couldn't swim more than 50m.

She, like others spoken to by RNZ, was accepting of the decision to cancel the swim.

"I can totally respect the fact the athletes' health and safety is of the utmost importance ... I'm a little bit gutted but that's just how it is."

Ms Reibe has another event lined up for early next year in Australia.

A spokesman for the half Ironman said the number of people registered who did not turn up to the race was fewer than 100.

They said there was always attrition on the day for a number of reasons, including injury or illness.