The Dusi: the very biggest of all paddle marathons...
They go large in South Africa.
The Dusi is a kayak marathon that has been held each January for over 50 years.
Over 1000 paddlers race 110 miles in 3 days to Durban. They use very narrow, tippy flatwater kayaks---yet there are many big rapids on this course. It's crazy! There are also many hilly, brushy portages.
Sadly, it's a bit tricky finding info at the race homepage, but there's lots of neat photos:
There are 2 other major kayak races in South Africa---the Fish River and the Berg.
Here's a good source for basic info on all 3 races: http://www.southafrica.info/about/sport/canoe.htm