The Dunedin series, which concluded on Wednesday night, has grown substantially since it began 15 years ago.
Event organiser Mike Harris said it had averaged about 65 swimmers across the 10 events held at Macandrew Bay and Vauxhall boat clubs this summer.
At its peak there were nights in early February which attracted 91 and 97 competitors.
That was a long way from the 30-35 people it attracted in a three-race series when it began in 2003.
It had grown every year since then and the past two years represented a peak.
While the brilliant weather this past summer had helped, Harris said it was an event now which attracted a wide range of people.
A lot of people who participated in the Challenge Wanaka triathlon - particularly those doing the swim leg in a team - had entered.
It was a good chance for them to practise swimming in the open water, as for some it was their first experience of doing so.
Surf life-saving clubs were also supporting the event, often bringing competitors along and then going out on their paddleboards afterwards.
It was popular among the masters age-group, and also attracted some of the top pool swimmers in the region.
The standard ranged from swimmers who were among the best nationally in the pool their age-grades to those just wanting to try it out.
Races were held over 500m, 1000m, 1500m and 2000m. In Wednesday night's 2000m race, the Danyon Loader Sport Otago Harbour Swim Trophy was at stake.
Tame Govaerts-Paul won the men's race and Erika Fairweather in the women's.
They swam the course from the Vauxhall Yacht Club in 24min 42sec and 25min 39sec respectively.
Fairweather was second overall in the 2000m race.
In the 1500m Annette Hunter claimed victory in 36min 13sec.
Cecilia Crooks won the 1000m race by nearly five minutes, turning in a time of 13min 07sec.
The 500m race was won by Kirsten Harvey in a time of 10min 10sec.
