The former Dunedin swimmer finished seventh in a stacked field in the women’s 800m freestyle, clocking a time of 8min 20.79sec.
It was her second-fastest time across the distance in her career and wrapped up her world championships, having made two finals.
Fairweather made a good start and was fourth at the first turn before battling for sixth with China’s Bingjie Li for the first half of the race.
The 21-year-old sat in seventh for the final 100m and pushed hard to come home with a good time.
United States great Katie Ledecky reminded everyone why she is the long-distance queen.
Ledecky had a good test against Australian Lani Pallister and Canadian Summer McIntosh for much of the
race.
She lifted the pace across the final 100m creating a gap between her competitors and stormed home in 8min 05.62sec to set a championship record.
Ledecky, 28, remains undefeated in the distance at the championships, winning a remarkable seventh title in Singapore.
Pallister boosted home for silver in an Oceania record time of 8min 05.98sec and McIntosh won bronze in 8min 07.29sec, in what has already been dubbed the greatest race over the distance.
"That’s pretty incredible, three of us going under 8:10," Ledecky said.
"I’m just really happy I could put that together.
"I don’t think I have anything to lose at this point of my career
"Everyone in that heat is the next generation of swimmers coming up — just proud to be a part of it."
On Friday, Dunedin swimmer Caitlin Deans finished 10th in the 800m freestyle with a personal best of 8min 28.72sec
"I’m absolutely rapt to come away with a PB," Deans said.
"To be so close to making the final is frustrating, but it’s just more motivation for the upcoming season."
Kiwi Finn Harland qualified for the men’s 50m backstroke semifinal after finishing with a personal best of 24.76sec in his debut world championships on Saturday.
The 19-year-old clocked 25.02sec in the semifinal to finish 16th overall.
Andrew Jeffcoat finished 27th with 25.09sec in the 50m backstroke.
Laura Quilter finished 22nd overall in the women’s 50m freestyle with a personal best of 25.08sec.
Defending men’s 400m IM champion Lewis Clareburt finished 10th overall in the event after clocking 4min 13.89sec in his heat yesterday.
Japan’s Tomoyuki Matsushita was the top seed heading into last night’s final with 4min 10.39sec.
