Swimming is a sport that attracts participants of all ages although it is largely a young sport. Competitions are organized by clubs, schools, and national associations. Short course competitions take place in a 25-metre pool, long course in a 50-metre pool. Olympic swimming competitions are over a variety of distances and strokes, and they take place in 50-metre pools. Synchronized swimming, waterpolo, and diving are also included in the Olympic programme. Swimming in the sea may be part of a triathlon race, and open sea races, including Channel swims, are also held. ‘Masters’ swimming competitions are held for those over 24 years of age whereas ‘veteran’ sports competitions in athletics are for the over 40s. Competitions for different age groups are held in most countries, and world championships also take place.