Just missed it this year. (Whew.)
September 8th, 2005 by Bob in Et Cetera
It should come as no surprise that this happens in the UK: Bog Snorkelling.
Competitors have to complete two lengths of a 60 yard trench cut through the peat bog in the quickest time possible, wearing snorkels and flippers (wet suits optional but advisable) but without using any conventional swimming strokes.
They also do it on mountain bikes.
Unrelated, but also in the UK: Table wrestling.