"This is not your traditional marathon event. In the toughest single-day expedition paddling race in the world, canoes, kayaks and paddleboards traverse two rivers systems, three lakes and 20 portages. It’s a total of 130 kilometers in less than 24 hours. No assistance, no support and no mercy. Each year more than a third of teams drop out."
Very detailed article with interesting pictures:
paddlingmag.com
The article is eight years old but the race is still being held. There will be a 58 KM ("sprint") and a the traditional 133 KM race on September 15-17, 2023.
Very detailed article with interesting pictures:

Why Muskoka River X Is The Toughest Paddling Race Ever
Over 130 kilometers, participants traverse two rivers systems, three lakes and 20 portages in less than 24 hours with no assistance, no support and no mercy. Ready to race?

The article is eight years old but the race is still being held. There will be a 58 KM ("sprint") and a the traditional 133 KM race on September 15-17, 2023.