Three friends from Winnipeg took on a challenge that's likely never been done before — swimming from the south Perimeter to the north Perimeter Highway in the Red River.

Pat Peacock, Taren Gesell and CBC's Jacques Marcoux are experienced athletes who had been training for months for the carefully planned 37-kilometre swim on Sunday.

"Why not try to challenge ourselves with something that, seemingly, is big and scary to show that you can do it," Gesell said before descending into the water early Sunday morning.

They expected the swim to take about 10 hours with short breaks along the way to refuel, but Marcoux said it went faster than anticipated.

One swimmer, Peacock, didn't complete the swim. He got out of the water early due to colder than average temperatures.

Afterward, snugly dressed in dry clothing instead of a dripping wetsuit, Gesell said the cold was the hardest part of the swim.

"The water was a lot, a lot tougher than we thought it was going to be," he said. "I think the averages for this time of year were about 10 degrees Fahrenheit warmer. I was borderline having to pull out before we even started."

Heading into the swim, Gesell told CBC News he expected internal mental chatter to be the biggest hurdle. He expected to ask himself, "Why are you doing this? You shouldn't be doing this. This is hard. you can just pull out, shore's right over there."

"It's a rush," he said when it was over.

"That's why we're doing this to feel alive, feel challenged, feel a little bit of fear and pain and uncertainty, and that makes you feel alive. Not everyone gets that in day to day life and to feel that, it's a lot of emotions."

The swimmers started the journey at around 6 a.m. Sunday morning in the Red River. They expect it to take about 10 hours. (Cliff Simpson/CBC)

While the swim was a personal feat for the friends, Peacock said he also hopes it reminds people how special the waters running through Winnipeg are.

"Just having people in the water makes people a little bit more aware of the water and the fact that we have all the huge rivers and wonderful resources running through our city," he said.

Steve Scoles says he thinks it's a bit crazy but he's excited to see the Winnipeggers complete the swim. (Cliff Simpson/CBC)

When the wild and wet adventure began around 6 a.m., Steve Scoles stood on the shore yelling support through a megaphone.

"I wanted to see the start of the swim. I mean, they are doing a 37-kilometre swim on the Red River and I think it's pretty crazy that they are doing this," he said.

"I think everyone thinks it is kind of semi-crazy but quite an accomplishment if they can do it."

Scoles added he didn't want to miss out on what could be a history-making swim.

"I don't think anybody has ever attempted a swim from Perimeter to Perimeter," he said.

The troupe of friends and family cheering at the finish line was a special moment, Gesell said.

"I said to the fellas in the boat who were taking care of me when I saw the final bridge, I said, 'What's that feeling? Feels like hope. I haven't felt that in 10 hours,'" he said.

"And that's kind of what it's like, it's just every emotion that you can imagine just all crammed into one."