The 49-year-old man is in Tauranga hospital. His condition was described as serious.
And a man was missing, presumed drowned, after being caught in a rip while swimming with friends in Titahi Bay, near Wellington.
The Westpac rescue helicopter, Mana Coastguard and the Titahi Bay Surf Lifesaving Club were combing the area for signs of the missing man last night.
Water Safety New Zealand boss Matt Claridge said he was particularly concerned at the number of swimmers who had drowned in open water events in recent years.
"We will be investigating this Taupo death very closely."
However, Swimming New Zealand chief executive Mike Byrne said there was a strong safety protocol in place at the event and the team responded appropriately.
About 500 swimmers competed in the day's events, which included races for Olympic through to recreational swimmers, in cool and choppy conditions on Lake Taupo.
Nine people lost their lives to drowning in New Zealand waters during the official holiday period - between Christmas Eve and January 5.
Claridge said Kiwis were heading to the water in greater numbers because of the hot weather and warned them to be extra cautious on the water.
"People are trying to make the most of their holidays and the warm temperatures and get out on the water, but they need to be reminded just how dangerous it can be."