At the 1974 British Commonwealth Games held in Christchurch, he won the gold medal in the men's 400m Individual Medley on the same day fellow New Zealander and Wharenui team-mate Jaynie Parkhouse won a gold medal in the 800m Freestyle.[3] Treffers would go on to claim a silver medal in the men's 1500m Freestyle, his main race, as he become just the seventh man in history to break 16 minutes finishing behind Australian Stephen Holland.
Olympic Games
He competed at both the 1972 and 1976 Summer Olympics with his best result being 6th place in the 1500 m at the 1972 Munich Olympic Games.