While most people would have shied away from physical activity after such an operation, Townsend said he finds comfort being in the water.
"I should have been a fish or had gills. I don't know why, but I've always felt so comfortable swimming."
He recalled his first swim in the National Series many years ago was the Auckland Harbour Crossing and acknowledged the 2.9km swim is a real challenge.
"I was never afraid of the water but it was good to see the finish line coming up - it always is."
Townsend only recently got back into the ocean and is taking a slow and steady approach to getting back to his best.
"I'll take it as it comes. I hope that I've got some swimming skills left. But I'm confident I can swim whatever distance."
Scott Rice, the event director of the State NZ Ocean Swim Series, said it is always a huge thrill seeing people overcome adversity and achieve their goals through swimming.
"It's great to see so many returning swimmers like Mike enjoying both the physical and the social side of the series," said Rice.
"I am looking forward to firing the starting gun for the 10th Harbour Crossing."
Townsend said one of the main reasons he has entered all six Ocean Swim Series events was the chance to get around the country and mix with like-minded people.
"It's the travelling. I like going away with a group and meeting more people my own age. It's very social."
In previous years Townsend has trained with a group of friends under their coach Carmel Dixon.
The group get together and train in a pool three times a week, followed by a swim in the ocean on the weekend, usually from Kohimarama to Mission Bay. Townsend will re-join the group for training later this year.
State Harbour Crossing
When: Sunday, November 17.
Where: Auckland.
Event Distance: 2.9km.
State Ocean Swim Series
1. Harbour Crossing, Auckland, Sunday, November 17.
2. Bay of Islands Classic, Saturday, December 7.
3. Capital Classic, Wellington, Sunday, January 26.
4. La Grande Swim, Christchurch, Saturday, February 22.
5. Sand to Surf, Mt Maunganui, Saturday, March 22.
6. King of the Bays, North Shore, Saturday, April 12.
For more information or to register visit www.oceanswim.co.nz.