['Canoe Marathon' (International Canoe Federation terminology) refers to both canoe and kayak marathon].
Perhaps the most gruelling and energy-sapping canoeing discipline. Paddlers race over distances along a minimum of 20km for men and 15km for women often on tidal flatwater and river estuaries. Competitions can be divided into stages or even days in extreme marathon events where paddlers can race over hundreds of kilometres of water.
Time-keeping happens at stages along the route, paddlers also have to endure portages - leaving the river and carrying their boat whilst sprinting on-foot around lock gates, weirs, shallow rocks and rapids.
Longer somewhat unstable boats are used for long distance cruising and sprinting.
Marathon is very much a community and spectator sport; thousands can line river banks for miles and miles, just like during cycling's Tour De France, cheering on their heroes.
It is not an Olympic sport, yet the closest it became to being so was in four Olympic Games (1936 and 3 post-war to 1956) where men competed in K1/2 and C1/2 10,000m flatwater sprints (note C1 was added in 1948).
Nowadays, following a series of international events, marathon paddlers compete in a World Championship and a World Cup event, both of which take place yearly over 20-30kms.