McMillan (26) was a member of the Cromwell club when he began his competitive swimming career as a teenager.
He transferred to Dunedin to be coached by Duncan Laing and boarded at Otago Boys' High School hostel.
His career progressed under the coaching of Laing and he became a New Zealand representative. He transferred to Auckland after Laing gave up coaching because of ill health.
McMillan competed for the North Shore club and was coached by Swimming New Zealand's head coach Jan Cameron.
He failed to make the grade in the pool but made his mark in surf life-saving and competed for New Zealand in that sport. He also competed in ocean swimming.
McMillan is ranked top in his specialist 200m butterfly, with a time of 2min 0.46sec and is poised to bring a gold medal back to Otago.
He is also ranked fourth in the 200m freestyle (1min 51.30sec), third in the 100m freestyle (51.16sec) and third in the 100m butterfly (54.1sec).
The six-day championships at the Henderson Aquatic Centre double as Olympic trials. A swimmer must reach the qualifying standard in the final to be selected for London.
Another top Otago contender is Troy Balvert (Waves), in the men's 800m freestyle, where he is ranked second, with a time of 8min 22.89sec.
Balvert, who had success in ocean swimming over the summer months, is also competing in the 1500m, where he has a best time of 15min 59.88sec.
Kate Godfrey (Neptune) is ranked fourth in the women's 400m individual medley (4min 59.58sec) and sixth in the 200m backstroke (2min 16.10sec).
Other Otago swimmers with a high ranking are Kurt Crossland (Neptune), sixth in the 100m backstroke (56.51sec) and fifth in the 50m backstroke (26.22sec), Matthew Glassford (Neptune), fourth in the 200m breaststroke (2min 17.46sec), and Katie Kenneally (Neptune), fourth in the 200m breaststroke (2min 35.87sec).
On the national scene, talented Wellington swimmer Natasha Hind (22) is looking to come out from behind the shadows instead of being regarded as a relay specialist.
Hind anchored the women's 4x200m relay team that won the silver medal at the Delhi Commonwealth Games and at the world championships in Shanghai last year, where its eighth place qualified the relay for London.
"I would like to make the team as an individual in the 200m freestyle," she said.
"Lauren [Boyle] has qualified a spot there now. But there's a second spot. So, if I can get under that individual Olympic A qualifying time, I would be happy."
