What is marathon canoe racing?

I like the Minnesota Canoe Racing Association's answer to this question:

Marathon canoe racing is a sit down style of paddling over a distance that varies from a few miles to over 100+ miles in one day including multi-day races. Some of these races may include some portages. The races can be held on lakes and rivers. The rivers are mostly calm but they can have some rapids of moderate difficulty with clear passage that may require some maneuvering. The larger races may have several classes whereas the smaller races there may be only a couple classes. These classes can be based on age and sex of the paddlers and the type of canoe.