Olympic swimming takes place inside a 50-meter-long pool divided into eight lanes. Swimmers race each other at distances varying from 50m (one lap) to 1500m (30 laps) using one of four strokes: freestyle, backstroke, breaststroke and butterfly (medley events use all four). All swimmers competing in a given race start simultaneously at the sound of a tone. The winner is the first to touch the wall of the pool after swimming the set distance.

There are 35 total Olympic pool swimming events: 14 individual events per gender, three relay events per gender, and the mixed medley relay.

How do swimming races start?

For freestyle, breaststroke, butterfly and individual medley (IM) events, swimmers begin by diving into the water from an elevated starting platform. On the starter's command, "take your mark," each swimmer assumes a starting position, arched over the knees and grasping the front edge of the platform. When all swimmers are still, the starter activates an electronic tone to start the race, and the competitors dive into the pool. Once in the water, a swimmer's head must break the surface within the first 15 meters.

For backstroke events, as well as the start of the medley relays, swimmers start in the water, facing the wall of the pool. They grasp a bar underneath the starting platform with both hands, and place both feet on a "backstroke ledge,” which dangles on the wall below the surface. When the race starts, swimmers dive backwards, launching themselves off the wall.

What happens if a swimmer starts prematurely?

In swimming, there are no "false start" warnings. Any swimmer who dives into the pool before the starting signal is automatically disqualified. If the starting signal sounds before the disqualification is declared, the race continues, and the swimmer is disqualified when the race is over.

How many laps do swimmers complete per race?

In swimming, the term "lap" is used to indicate a single length of the pool. Olympic swimming utilizes a "long course" pool, meaning each lap is 50 meters. The amount of laps required to be swam in a given race depends on the total distance of the event. The shortest Olympic swimming event, the 50m freestyle (affectionately known as the "splash and dash"), requires just one lap from one end of the pool to the opposite end. Races of 100m in length require two laps: one end to the other, and back again. The longest Olympic event, the 1500m freestyle, requires 30 laps of the pool.

How do swimmers turn between laps?

Quick turns are essential in any event over 50m in length. In every stroke discipline, swimmers must make contact with the wall as they turn. In freestyle and backstroke, swimmers may somersault as they reach the wall, touching it only with their feet. In butterfly and breaststroke, swimmers must touch the wall with both hands simultaneously before executing the turn. Once a turn is made, swimmers can remain underwater for up to 15 meters before they must resurface and continue performing the required stroke.

Four different strokes are contested at the Olympic Games. They are: freestyle, backstroke, breaststroke and butterfly. Detailed explanations of each can be found HERE.

There are also two individual medley (IM) events per gender, 200m and 400m. They require athletes to swim each of the four strokes for one-quarter of the race, in a set order. That order is butterfly, backstroke, breaststroke and freestyle.

There are some major differences between how swimmers approach the different races of the Olympic program. The sprint races (50m and 100m) are all-out effort from start to finish. The slightest mistake can cost a swimmer a fraction of a second, and thus the race.  

The 200m events require swimmers to have a sense of pace as well as the ability to swim a controlled sprint. This distance is considered by many to be the most difficult to master.  

The distance events – the 400m, 800m, and 1500m freestyles, along with the 400m IM – require swimmers to constantly be aware of their position in a race and to closely monitor their fatigue. Swimming the first portion of the race too fast can sap a swimmer's stamina and cause a poor finish, while swimming the first portion too slowly can result in a deficit too large to make up.

Swimming becomes a true team sport during relay events. Countries field teams of four swimmers, each of whom must swim a quarter of the total length of the race. The second swimmer is only able to begin his/her leg once the first swimmer touches the wall to complete theirs, and so on. The winner is the country who’s fourth-leg swimmer touches the wall before any other country’s fourth-leg swimmer. 

Relays are contested over a prelim and a final. The athletes who swim in the final do not necessarily need to be the same ones who swam the prelim. Strong swimming nations often bring “relay-only” swimmers to the Olympics to swim in the prelims but not the final, in order to keep the best four swimmers rested for the final. Relay prelim swimmers do qualify for a medal should their country win one in the final, meaning as many as eight athletes can win medals for a single nation in a relay event.  

What relays are there at the Olympics?

There are seven total relay events at the Paris Olympics: two freestyle relays per gender (4x100m and 4x200m), one medley relay per gender, and the mixed medley relay which includes teams of two men and two women. 

What is the difference between a freestyle relay and a medley relay?

In a freestyle relay, all four swimmers swim using the freestyle stroke. In a medley relay, each of the four swimmers uses a different stroke. The order of the medley relay goes backstroke, breaststroke, butterfly and freestyle. This is standard for all medley relays, regardless of gender.

The 10k open water event (also known as the "marathon swim") is held in a natural body of water and follows a wide course with no lane restrictions. Incidental contact between swimmers is permitted and expected, especially during the mass start, when all 22 competitors set off at once. 

During the 10k competition, each athlete must wear a wristband known as a transponder, which is linked to the timing and results system. Athletes can be disqualified for pacing, slipstreaming, walking or jumping, or finishing without their transponder. The athletes are also identified by temporary tattoos or markers on their upper arms, shoulder blades and wrists.

There are two open water races at the Olympic Games, a men's race and women's race. At the 2024 Paris Olympics, the races will take place in the Seine river through the heart of Paris.