Synchronised Swimming is basically gymnastics in water. Competitors are judged on how well they perform as either a team, duet or individually and it isn't as easy as they make it look.
An individual routine lasts for three minutes and at least half of that is spent under the water. Every part of the routine is choreographed to the beat of the music you choose to perform to.
They even have speakers in the water so that you can hear the music!
Duet performances last three and a half minutes with each swimmer performing exactly the same routine all the way through, and it takes a lot of training to get it right.
Team routines can have up to eight people involved and last four minutes. The team will perform what is called a lift - someone will be thrown up out of the water and will perform some kind of special move like a somersault or a back flip!
Competitive synchro swimmers must be extremely fit, and completely at home in the water. You must be strong yet graceful and have stamina and determination.
Boys can take part too, it's not only for girls!