Swimming events take place in a pool 50m long and 25 metres wide, divided into 10 lanes, of which the eight in the middle are used for competitions, one for each swimmer. The pool must be at least two metres deep. Races range in distance from 50m (one length) to 1500m (30 lengths) in all four strokes backstroke, breaststroke, freestyle and butterfly - and a combination of them, the medley. Relays comprise four different swimmers, each swimming in sequence for one quarter of the total distance.
Swimming competition is controlled by strictly observed rules applied by the International Swimming Federation, FINA.
Breaststroke, the slowest stroke, involves swimming with the body face down and flat on the water, with the arms pulling and recovering together underwater.
Butterfly is similar, but with the arms recovering together above the water in combination with a dolphin kick, obtaining greater speed.
Backstroke is swum on the back with alternate arm strokes and kicking.
In freestyle, the fastest of all the swimming strokes, swimmers use alternate arm strokes and different kick pace, facing the pool bottom.
The medley combines four strokes in one race, with each stroke taking up an equal part of the distance. The swimmer first swims butterfly, then backstroke, then breaststroke and then freestyle.