How does the start work, and what happens with a false start?

Start procedure (World Aquatics Rule 4):

• Freestyle, breaststroke, butterfly and individual medley start with a dive; backstroke and medley relays start in the water.
• The referee blows a short series of whistles (swimmers get ready at the starting end), then a long whistle for swimmers to take their position on the platform. For backstroke the long whistle means enter the water, and a second long whistle means return to the starting position.
• The referee signals to the starter with an outstretched arm, held until the starting signal. Swimmers are now under the starter's control.
• On "take your marks" swimmers immediately take up a starting position (for a dive start, at least one foot in contact with the front of the platform). When all are stationary, the starter gives the starting signal.

False starts:

• A swimmer who initiates a start before the signal may be disqualified (Rule 4.4).
• If the signal has already been given, the race continues and the swimmer is disqualified at the end.
• If the disqualification is declared before the signal, the signal isn't given, the others are told "stand down please", and the start is repeated from the long whistle.
• Under Rule 2.3.6 the referee disqualifies for an early start observed and confirmed by the starter and the referee, reviewing the footage where automatic officiating equipment is available. World Aquatics' August 2026 commentary clarifies that the referee and starter are not required to concur, and the referee's decision after review is final.