"We can only hopefully go up from here and it's the start of a massive year for me so I've just got to keep on building and getting stronger and stronger."
Meanwhile, in the women's 10km event on Saturday Penelope Hayes (Cambridge) stole the title from race favourite Charlotte Webby.
It was only her second 10km ocean swim event.
Hayes, a triathlete, competed in her first 10km open water swim two weeks ago in Penrith and was surprised but pleased with her victory on Saturday.
"It was a goal to win but I didn't know if it was possible or not. It's only my second 10km so I still don't really know what to expect when I go out there. It was a bit colder than Penrith a couple of weeks ago.
"I've had a stress fracture in my foot since July so I haven't been able to run and it just provides a racing opportunity away from that."
Hayes also won the 5km race yesterday to make it a double for the weekend.
The national open-water championships, which were held as part of the Epic Swim event, are the first stepping stone in the process towards qualifying for the World Championships in July.
Results:
Men 10km: 1 Kane Radford (Rotorua) 1:58:40; 2 Phillip Ryan (Waterhole) 1:58:45; 3 Liam Albery (Capital) 1:58:45
Women 10km: 1 Penelope Hayes (St Peter's) 2:10:04; 2 Charlotte Webby (Aquabladz, New Plymouth) 2:15:09; 3 Caitlin Delany (Tasman) 2:21:48
Men 5km: 1 Kane Radford (Rotorua) 59:27; 2 Phillip Ryan (Waterhole) 59:28; 3 Liam Albery (Capital) 59:30
Women 5km: 1 Penelope Hayes (St Peter's) 1:08.21; 2 Bridget Maher (West Auckland) 1:08.23; 3 Abigail Chapman (Pukekohe) 1:08.38