There are many swimming events at the Olympic Games. There are four strokes.
They are the freestyle, breast stroke, backstroke and butterfly. In each case, the swimmers use their arms and legs to move through the water.
In some events, called medleys, the swimmers must swim all the different types of strokes in one race.
At the first modern Olympic Games in 1896, the swimmers raced in the sea. Now, they race in an indoor pool.
Swimming races can be one lap of the pool or up to 30 laps.
The United States has dominated Olympic swimming.
