An outbreak of toxic algae in Lake Taupō has forced New Zealand Ironman organisers to drop the swim leg from Saturday's 70.3 Taupō half Ironman.
Race officials got the warning after scientists reported the presence of the dangerous organism at five different locations - including Phormidium at areas within Five Mile Bay, Acacia Bay, the main lakefront in Taupō , Whakaipo Bay and Kinloch Beach.
With the swim leg scrapped, the race will start with a 3km run, followed by a 90km bike ride and then a 21km run to finish it off.
New Zealand Ironman regional director Chris Randle said this is a first for the Ironman.
"It has never happened to us before. It is not a regular occurrence and the team is still optimistic about delivering a fantastic event on Saturday.
"We had a letdown last night, but we are working hard to make sure everyone has a great experience."
Race director Wayne Reardon said organisers immediately rushed to alert competitors to the changes and what options were open to them.
"We know athletes will be disappointed," he said.
"However, our team are still committed to putting on a fantastic race on Saturday, albeit in a modified format."