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 athlete 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.