Prescott (60) defies his age by his ability to dominate the open-water swim on Otago Harbour at the Masters Games.
He had his sixth consecutive win in the 3km race on Saturday morning in a time of 35min 47sec.
He was followed home by fellow Dunedin Masters swimmers Richard Jongens in 37min 22sec and Steve Sexton in 38min 47sec.
Prescott has now won the race on the two-lap course from Vauxhall eight times.
The women's race was won by Dunedin City Council policy analyst Anne Gray (49) in 41min 19sec from Otago University technician Katie Price (41) in 41min 57sec.
It was the first time Gray had won the race and it was a reversal of the position two years ago when Price won and Gray was second.
''It was pretty good conditions,'' Prescott said.
''It wasn't too rough.''
The hardest part for Prescott was getting into a rhythm again after the faster pool swims during the week.
''It always takes time to get into a rhythm so you can keep going,'' he said.
Prescott, the aquatics manager for the Dunedin City Council, was well into his rhythm by the time he went round the top buoy on the first of the two laps.
He led Jongens by 28sec and Sexton by 52sec. Prescott's margin had increased to 49sec at the end of the first lap and to 1min 33sec at the top mark on the second lap.
The tide was flowing Prescott's way as he sped down to the finish to win by 1min 35sec.
There were solid swims by Jongens, a Dunedin geologist, and by University of Otago education lecturer Sexton.
''Steve is always able to get ahead at the start and it is hard to catch up on him in the harbour,'' Jongens said.
''Positions were decided by the first buoy.''
It has been a successful week for Prescott ,who also broke six New Zealand masters records in the pool in the 60 to 64 grade.
They were 100m (1min 21.44sec) and 200m (3min 00.92sec) breaststroke, 200m ( 2min 15.62sec) and 400m (4min 45.47sec) freestyle, 200m (2min 40.49sec) individual medley and 200m (2min 39.61sec) butterfly.
Prescott trains hard each week under the direction of his coach, Gennadiy Labara, and has six sessions in the pool. He also does cycling and running.
During the summer months he has one session a week in the harbour over 3km.
The younger swimmers in Labara's squad impress Prescott.
''I'm in awe of the young kids with how much they train and how well they are going,'' Prescott said.
''They always give me a bit of banter about being the old man.''
Brent Cardno (Dunedin) won the 1500m swim in 21min 19sec from Joel Tyndall 23min 25sec. Helen Cassidy won the women's race in 23min 32sec with Kristy Eyles second in 24min 52sec.
The oldest swimmer to complete the 1500m race was 70-year-old Jonathon Pascoe (Christchurch), who finished in 34min 35sec.
Lydia Harrington won the 500m race in 17min 39sec from Jane Dickison in 17min 45sec.
Games ambassadors Nina and Lisa Daniel both completed the 500m swim. They also competed in bowls, curling and shooting.