Nicknamed and known simply as "The Marathon," it first ran in 1947, and is perhaps the oldest marathon canoe race in the United States, and is the longest, non-stop, canoe-only race in North America. The race has been billed as "The World's Toughest Spectator Race" as many of the spectators follow the racers overnight down the full 120 miles (190 km) to the finish.
Since 1971, the race has been held during the last full weekend in July, during Grayling's annual Au Sable River Festival. To determine the starting position of the racers for the night of the Canoe Marathon, there is a sprint held to determine which of the teams is fastest or slowest. The sprint trials are held at Penrod's Canoe Livery. The trials are held the Wednesday, Thursday, and Friday before the race on Saturday. Each team will head upstream one quarter mile towards the Old AuSable Fly Shop. Once there you must complete a counter clockwise turn around a buoy.
Then you must head back downstream to the starting point and the next team does not start until the team finishing reaches a point close to the start buoy. On average this can take from 2 minutes and 15 seconds to 5 minutes. The overall finish times range from about 4 minutes and 30 seconds to 13 minutes. While they are on their way back to the starting buoy they must maintain the number of buoys on the left side of their canoe. Once all of the teams have finished the sprint trials they will be lined up in groups of five, from fastest to slowest, on the night of the Marathon, to make the 910 ft (277 m) LeMans-style foot race that starts the race.
The Marathon starts at 9:00 P.M. in Grayling in a LeMans-style start where the competitors carry their canoes in a footrace four-blocks through town to the Au Sable River entry point. Upon reaching the Au Sable River, they begin paddling non-stop throughout the night. In addition to paddling for 14–19 hours non-stop overnight, competitors must also make portages around six hydroelectric dams along the river race route.
To participate in the race the competitor must be at least the age of 15. In order to enter by July 1st there is a $220 fee. To enter by July 15th, the fee is $320, and to enter by July 25th the fee is $420. However, the fees are all worth their prices because upon completing the race the canoers are awarded cash prizes. The reward for first place is $5,000. Second place is $3,500, and third place receives $2,500. Even if a racer finishes in 40th place, they will receive $230 which is more than their entry fee. Competitors that finish after 40th place will receive a finishers metal.
The race relies on the efforts made by many volunteers, and is organized and ran by an all-volunteer non-profit organization: AuSable River International Canoe Marathon, Inc.
According to wikipedia