The 13-year-old Neptune competitor swam 4min 57.81sec at the club's 34th annual Queen's Birthday meeting at Moana Pool, to break
the previous record of 4min 58.09sec held by Auckland's Yeonsu Lee.
Fairweather also claimed gold medals in the 13-14 aged 100 and 200m IM, as well as in the 200m freestyle.
She took home silver in the 50m freestyle and 200m backstroke, and bronze in the 200m butterfly.
The meeting attracted 416 swimmers from 27 different clubs.
Of those, 41 came from the host club, which won its share of medals.
Two of its national swimmers, Andrew Trembath and Courtland Ellis, had a close duel in the 17 and over 100m freestyle.
Ellis swam 52.12sec, pipping Trembath by 0.16sec to claim the title.
Fellow Dunedin swimmer Tame Govaerts-Paul, of Zenith, finished third.
The trio had a good weekend and featured prominently among the medals in the open age-group.
In the open women's age-group, Neptune's Caitlin Deans proved near unbeatable, winning gold medals across the freestyle, backstroke and individual medley.
