"I missed winning an Olympic medal at Atlanta but I'll accept this trophy. This win means a lot," said Allen, 23, holding the Roughwater Swim trophy high above his head after finishing first in the men's field in his first try.
Gartrell, 19, who competed in Atlanta and who also missed out on a medal, happily hugged her monkeypod bowl presented to the first women's finisher.
"My first Waikiki Roughwater and I didn't know the course. I felt lucky to have won," said Gartrell, who led from start to finish.
Because of an adverse current, the 2.4-mile plunge, which began at Kapiolani Park's San Souci Beach and finished at Duke Kahanamoku Beach, was one of the slowest and most difficult in the history of the race.
The swim drew 998 participants. Those not able to make headway against the fast-running current were hauled from the water by crews from accompanying escort boats.
Allen rounded the final marker in third place, then caught a wave and surged to the front.
"Successfully riding that wave made the difference," he said.
Allen completed the course in 51 minutes, 11 seconds, well shy of the men's record of 42:13.
Kurt Eldridge, 22, also from Australia, placed second in 51:58.
Gartrell finished ninth overall in 56:58, 11:25 off the women's record.
Though the Aussies swept the top awards, noteworthy performances were turned in by locals.
Honolulu swimmers, Jodi Jackson, 19, and Pia Chock, 17, finished second and third, respectively, among the women. Carl Larsen, 18, finished fourth in the men's race, the best of any local resident.
"I was going great until I got pounded by a wave then surfaced pretty disoriented," Jackson said.
The former state high school swim champ from Punahou, now starting her sophomore year at Stanford University, finished 17 seconds behind Gartrell.
How rough was yesterday's Waikiki Roughwater?
John White Cater, 64, and the only participant to have completed all 27 Roughwater races, said yesterday's contest was his second-toughest swim (1985 was his hardest).
"I was really happy when my race was finished," said Carter, whose time was 2 hours, 50 minutes.
For Eric Roeder, paralyzed from the chest down, just finishing yesterday's swim was a challenge.
"The only lower body movement I have is an occasional wiggling of my toes," he said. "The current was strong and against me, but I would never drop out." Roeder finished in one-hour and 38 minutes.