Tasmania Police report the man from Queensland was on the first day of a planned two-week trip around the harbour when his kayak began to take on water about two kilometres south of Strahan about 11.20am.

"He attempted to swim towards shore but was overcome by the cold waters," Strahan Constable Wayne Bradford said.

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"He transmitted a distress call on his handheld VHF radio when he realised that he wasn't going to make it to shore."

Petuna's Stephen Gill was bound for Strahan after a morning feeding when he heard the distress call.

"Tas Maritime radio coordinated a search for myself and the Tassal dive vessel to conduct in the northern area of the harbour, near Smiths Cove," Mr Gill said.

"I only just managed to see him.

"He was struggling to swim and his kayak was full of water.

"He was very cold and shaken up.

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"I got him onto my vessel and took him back to West Strahan beach where we were greeted by Tasmania Police."

Mr Gill said it was a matter of being in the right place at the right time.

"It's lucky for him that we were nearby, another 15 minutes and it may have been a very different outcome," he said.

The kayaker was treated for mild hypothermia.

"It would only have taken him getting cramp or the fish farm boats being further away and this would likely have been a tragic outcome," Constable Bradford said.

Tasmanian Salmon Growers Association's Angela Williamson said the rescue was an act to be proud of.

"When you hear someone's in trouble and in the water, it's tools down and you do all you can to help them," she said.

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