One of the biggest events in Cambodia for swimmers is the annual Mekong River Swim. Since most Cambodians would not dare attempt, it ends up being largely an expat event.
This year, about 150 people participated in the race. Everyone lines up on the riverbank, the megaphone screams 'go' and everyone beelines it for the other side. Two things to watch for – beelining for the other side usually means you get pushed by the current downstream so make sure to compensate along the way. Also, fast speed and inexperience leads to a large consumption of Mekong water, which I can assure is far below potability standards.
When all the results were in, I placed #68 (about 16 minutes) which is pretty bad but not embarassing concidering no preparation or training whatsoever. More information at Mekong River Swim