What is marathon swimming, and how is it won?
B · Beginner · The race · 1 of 4Marathon swimming is the Olympic name for the 10 km race in open water swimming: a mass-start freestyle race in a river, lake, sea or channel. Swimmers follow a course marked by buoys and finish by touching a plate at the end of a funnel. The world championships add a 5 km race, a mixed relay and a knockout sprint.
How it works
- What it is: "any competition that takes place in rivers, lakes, oceans or water channels or any other body of open water".
- The Olympic event: 10 km for men and for women.
- World championships: 10 km, 5 km, a mixed team relay of 4 x 1500 m and, where agreed, a 3 km knockout sprint.
- The stroke: "All Open Water Swimming competitions shall be Freestyle events".
- The course: competitors must complete the whole of it, "respecting all designated turn buoys and course boundaries".
- The start: everyone together, from a fixed platform at the main events.
- Feeding: drinks are handed over from a platform by pole or by hand.
- Penalties: a yellow flag for a first infringement and a red flag, which means disqualification, for a second.
- The finish: a touch on a finish plate at least 5 m wide.
- Timing: by a transponder on each wrist, recorded in tenths of a second.
- Minimum age: 14 on 31 December of the year of competition, at the Olympic Games and world championships.
Tricky cases
Is the Olympic marathon swim 42 km, like a running marathon?
No. It is 10 km.
Can a swimmer use breaststroke or backstroke?
Yes. The races are freestyle, which in swimming means any style may be swum.
Is the course always a loop?
No. The rules ask only that the course is surveyed and marked and that every turn is shown. Championship courses are laps round buoys so that the swimmers pass the feeding platform several times.
Why the rule exists
Open water has no lanes, no walls and no two courses alike. The rules cannot make conditions equal from one race to the next, so they concentrate on what happens between swimmers: who may touch whom, who may be helped and how the finish is judged.
Where it differs
| Where | What changes | Source |
|---|---|---|
| World Aquatics rules | As above | OWS 1; OWS 5.1 |
| Pool swimming | Lanes, walls and times to a hundredth of a second | Swimming Rules |
| Junior championships | 5 km for ages 14 and 15, 7.5 km for 16 and 17 and 10 km for 18 and 19 | OWS 1.5.2 |
| Triathlon | The swim is one leg of three and has its own rules | World Triathlon rules |
From the rule book
World Aquatics, Competition Regulations, Part Three: Open Water Swimming Rules (in force as from 1 January 2025), Articles 1.1 to 1.5, 4.1, 5.1, 5.3, 5.13, 6.3, 6.4 and 9.2.1. Checked 14 October 2026. Official document: World Aquatics Competition Regulations (PDF).