Among the men on their marks on the beach is Serbian-born Milos Zvijer, who is shifting uneasily from foot to foot and edgy about talking to me in case he misses what he's waiting for. It's his first time, he tells me, and "it is a very big thing for us. It's on this day John baptised Jesus".
"It's happening in our country too right now, but it's the middle of winter and they have to swim in the cold. For us" - he smiles at the 23C heat - "it's very easy."
Quite what "it" is, I'm about to find out. Watched by a crowd of 100 or so who've turned up for the occasion, the head priest, Father Pavlos Patitsas, has lowered a 40cm high wooden cross twice into the water. Then he throws it 20m or so out into the water, which almost instantly turns to frenzied, churning foam as the beefy blokes head for it. I think briefly and sympathetically of the swimmers in Russia.
There's too much commotion to pick what's happening out there, though I suspect the tactics are closer to ice hockey than gin rummy. But within moments, 43-year-old Alexander Zapisetskiy holds the cross triumphantly aloft, prompting a cheer from the Russians in attendance; the Greeks, if they are grumbling, are far too polite to do so audibly.
Zapisetskiy kisses the cross, and holds it out for all the other swimmers to kiss too: it's a ritual that will be repeated all over the world in the 24 hoursthat follow.
I came to Devonport at the invitation of Patitsas, after visiting him in his small and modest church in Western Springs. The letterbox had caught my eye: a decommissioned LPG cylinder with a cross on top, it seemed altogether too whimsical to be passed by.
Ohio-born Patitsas was a welcoming host whose face was fixed in a permanent beaming smile . He showed me into his church - it's remarkably roomy inside and boasts some beautiful icons in the serene front-on Byzantine style that anyone who has visited Asia Minor will recognise - and in his soft Midwestern tones, explained that he saw Orthodox Christianity as based on continuing the teachings of the early apostolic church.
There are many national brands, so to speak: Greek and Russian are the big hitters but Serbia, Romania, Ukraine and Bulgaria are among the 14 nationalities in the confederation.
"We certainly have more in common than what distinguishes us," he says.
"Different churches respond to the needs of their people and there are differences of emphasis."
Patitsas had hoped to introduce me to his Russian church counterpart, Father Vladimir Boikov, but it appeared he was feeling poorly.
"Of course I'm feeling poorly," he told me in a booming Ocker twang when I caught up with him after the Blessing of the Waters.
"I'm an Australian and I have to live in New Zealand."
He was winding me up, of course.
Sydney-born of "trans-Siberian Cossack" parents who had fled the communists first in Russia and then in China, Boikov says the Russian community here is small.
"About 15,000 Russian-speaking people have arrived here in the past 20 years, most in Auckland," he says. "But very few are Christians. A lot are baptised but never go to church, the same as in Russia.
"You have to understand that we have suffered a lot from 70 years of communism and atheism. There is a searching for faith, but it's a very slow one."
