He dedicated the victory to former clubmate Mitchell Walker.
The body of Walker (22), a tourist guide, was found in the Greenstone Valley last week. It is thought he died after falling while descending from a ridge.
"Our club members were devastated by the news," Queenstown coach Frank Wylie said.
"We were determined to come here and dedicate our performances to Mitchell."
In 2004 Walker became the first Queenstown swimmer to compete at the national open championships when he contested the 50m and 100m breaststroke.
He competed for the Queenstown club from 1998 to 2005 and also contested the Olympic trials in 2004.
Walker also won medals at national age-group championships in the 50m and 100m breaststroke.
Fea's win was the highlight of the night for the Queenstown club. He took the lead out of the blocks and hit the water flying to record a time of 26.09sec.
It was the second-fastest time of his career.
Nick Tyrrell (Neptune) was second in 26.89sec and Braden Doyle (Waves) third in 28.09sec.
Fea (17), a butterfly specialist, has won the open 50m butterfly at three major provincial championships this season, in Auckland, Canterbury and now Otago.
Fea emulated his brother Josh (19), who achieved the treble at provincial championships in 2003.
Josh Fea won the boys aged 12 and 13 50m freestyle at the Auckland, Southland and Otago championships.
Fea's efforts pleased Wylie. "McGregor's matured a lot in the last two years. When he steps up to the blocks he's ready to race."
The Queenstown club brought 39 swimmers to the Otago championships and there was a determination about their performances.
In the morning heats the Queenstown swimmers achieved 65 personal-best performances and reached 43 finals.
Last night the Queenstown swimmers won six titles, with the other outstanding performance coming from Marc Lemaire-Sicre, who won two titles in the boys aged 14 and 15 grade.
He swam personal-best times when he won the 50m butterfly in in 28.48sec and the 100m backstroke in 1min 05.85sec.
He was challenged all the way in the 50m butterfly by Kieran Applegarth (Waves), who was second in 28.64sec.
The other Queenstown gold medals went to Mitchell Mawhinney in the boys 9 and under 100m backstroke (1min 44.22sec), Patrick Harris in the boys aged 10 and 11 100m backstroke (1min 20.97sec) and Lauren Kerr in the girls aged 12 and 13 200m breaststroke (3min 03.92sec).
Matt Henderson (Wanaka) just failed to break the oldest record in the Swimming Otago books when he won the boys aged 11 and under 200m breaststroke in 3min 05.75sec.
Jeff Conroy set the record of 3min 05.20sec in 1971.
Lil Clearwater (Neptune) broke her own Otago girls aged 14 and 15 record with a time of 1min 09.05sec in the 100m backstroke.
William Hurst (Oamaru) won the boys aged 12 and 13 100m backstroke in 1min 12.78sec and Callum Stammers (Milton) the boys aged 14 and 15 200m breaststroke in 2min 45.46sec.
