At least one secondary pupil fainted and others retched on the finish line as temperatures hit the 30s at a Central Otago triathlon yesterday.
Witnesses said a lack of drinking water around the course in Cromwell led some competitors to drink from the lake.
The pupils were taking part in the Otago Southland Secondary Schools Triathlon Championship at McNulty inlet.
There were anecdotal reports of students vomiting, both around the course and after finishing.
A team from East Otago High School said water should have been provided and they felt some competitors had been drinking out of the lake as their only option to keep hydrated.
But all competitors and schools had been warned about the conditions and told to bring adequate water. Otago Boys' High School teacher Kelvin McCrone said it would have been good to have had a water tanker so competitors could refill drink bottles.
''It was hot, all right,'' he said.
Mt Aspiring College assistant principal Simon Nyhof said it was the responsibility of teachers and support crew to make sure the children were properly supplied.
Event controller and Sport Central co-ordinator Bill Godsall agreed it was hot, ''especially for kids that aren't used to it''.
Due to the heat, the cycle section was shortened from 20km to 15km, he said.
A collision near the transition area led to one senior girls' team competitor, Holly Pierce, of James Hargest College, needing treatment by St John after she fell from her bike.
A St John spokesman said the girl was taken to the Cromwell Medical Centre.
Mr Godsall said she ''will be OK'' and the incident was caused by ''a moment's inattention'' as she waved to friends.
He said numbers were up on other years with about 320 pupils competing yesterday.
''I think it was the best performance I've seen of any athletes on our roads recently,'' he told the pupils after the race.
The Otago Boys' High School senior boys team of Michael Gray, Lachie McGregor and Ben Wardhaugh were the first to finish in 43 minutes 14 seconds.
The first individual competitor to cross the line was Mt Aspiring College junior Janus Stranenberg in 46min 16sec.
