I read years ago about a Dutch activity/sport called mudwalking.
Apparently, Holland has lowland, actually below sea level marshes, where a
man walking sinks into a combination of water, mud, marsh, sand, and silt,
sometimes up to his neck. Terrain of this sort connects a number of islands
and peninsulas. There are foot races between these outcrops of land.
Supposedly, the sport is dominated by very tall men, as they can pass
through terrain that shorter individuals cannot.

Is this an accurate description of the sport? Is it still popular? Is it
highly competitive?

In England, they have the Fens runners; foot races compete through marshy
terrain, though above sea level. Races go on for days.