How swimming works at the Olympics

HOW SWIMMING WORKS AT THE OLYMPICS:

* The swimming pool is 50m long, 25m wide and 3m deep

* It is divided into 10 lanes, although only the centre eight are used for competition

* There are four strokes used in Olympic competition: freestyle, breaststroke, butterfly and backstroke

* All four strokes feature in the individual medley and medley relay events and swimmers also compete in the freestyle relay events

* Olympic races in the pool are conducted over a variety of distances, from 50m to 1500m

* The first swimmer to touch the electronic finishing touchpad at the end of the pool is the winner

* Events start with heats, the number of which depends on the number of swimmers in the event, with athletes seeded according to FINA rules

* For 50m, 100m and 200m events, the top 16 swimmers from the heats progress to the semi-finals, and the top eight from these compete in the final

* As in the heats, the swimmers' seedings are used to decide which semi-final and lane they swim in

* In 400m, 800m, 1500m and relay events, swimmers progress from the heats straight to the final.