Trembath (17), a pupil at Otago Boys' High School, won the boys aged 17 and 18 100m backstroke at the national age group championships at Wellington on Thursday night.
His time of 56.83sec was a second faster than the qualifying standard for the event and qualified him for the Pan Pacs and the Youth Olympics in China. It was worth 763 Fina points.
It was a personal best time by Trembath but was short of the Otago open record that is held by club mate Kurt Crosland at 54.70sec.
Trembath took the lead in the first 15m to put pressure on his opponents and went on to beat Jackson Cropp (North Shore) by 1.83sec.
Trembath has the chance of representing New Zealand at three major international events this year. He has already been selected for the world surf life saving championships in Montpellier, France, in September.
The third night of the championships was a successful one for Otago swimmers who won three gold and a silver medal.
Tame Govaerts (Zenith) won his gold medal in the boys aged 14 200m breaststroke, in an Otago record time of 2min 29.42sec. It was his second Otago record at the championships. He broke the Otago record in the 50m breaststroke earlier in the week with his time of 31.54sec.
Campbell Pearson (Alexandra) won the boys aged 15 100m backstroke, in 1min 01.37sec, from Jack Anderson (United, Auckland), 1min 01.54.
Caitlin Deans (Neptune) won her third medal at the championships with a silver medal in the girls aged 14 200m freestyle, in 2min 08.71sec, a performance worth 676 Fina points.
Otago swimmers have won 12 medals - three gold, six silver and three bronze - after three days of the championships, which end tonight.
