After athletics, swimming is the sport that offers the most medals at the Olympics, with 32 events to be contested in the pool at Rio.
The action takes place at the purpose-built Olympic Aquatics Stadium, which will also host the finals of the men's and women's water polo competitions.
Unlike at London, the diving and synchronised swimming events will be held at a separate venue, the Maria Lenk Aquatics Centre, while the final swimming event, the 10km marathon, is being held in the waters off Copacabana beach.
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A brief history of swimming:
Humans have swum since prehistoric times, but swimming was not regarded as a proper sport until the 1800s and some of the strokes seen at the Olympics are relatively new - in the West at least, where most people swam breaststroke until the turn of the last century.
The crawl was devised from overarm strokes practised by North Americans and Pacific Islanders, as seen in cave paintings dating back thousands of years. But today's version is widely credited to Englishman Frederick Cavill, who settled in Australia and began to teach what became known as Australian crawl.
Butterfly was invented in the 1940s, when breaststrokers tried to increase their speed by bringing their arms forward out of the water. The move was immediately outlawed but gave birth to the new event, which made its Olympic debut in 1956.
Swimming at the Olympics:
Swimming has been a part of every modern Olympics since the Games were resurrected in 1896, when four events were contested in the waters of the Mediterranean Sea. Women were not allowed to compete until 1912.
Among the events to have been tried and abandoned over the years are the 200m obstacle race, in which swimmers had to clamber over and swim under rows of boats, and the underwater swimming competition, which was dropped as it did not offer much of a spectacle.
There have been many developments over the years. Separate breaststroke races (different from freestyle) were introduced in 1908, a standard 50m pool was adopted in 1924 and diving blocks were first seen in 1936. The 1950s saw the arrival of the tumble turn and butterfly stroke while goggles were allowed from 1976. Different designs of swimsuit have also come and gone - men only began to swim bare-chested in the 1930s and full-length racing suits developed in the late 1990s were outlawed in 2010.
Multiple medallists:
It is in the pool that some of the greatest ever Olympians have established themselves, partly because there is more scope to win several medals here than on the track.
Mark Spitz won seven golds at Munich in 1972, swimming butterfly and freestyle, but he was eclipsed by Michael Phelps, who won eight golds in the same two strokes in Beijing.
Do British athletes have a chance?
Not everything went according to plan for Team GB at London 2012. Set a minimum target of five medals they managed only three and none was gold. That in turn has affected funding, although the team go to Rio with several medal hopefuls.
Adam Peaty is the UK's best hope for gold. He swims in the 100m breaststroke and is the overwhelming favourite. Elsewhere, James Guy won gold in the 200m freestyle at the 2015 World Championships, while Jazz Carlin in the 200m medley and Siobhan-Marie O’Connor in the 800m freestyle won bronze medals.
Who to watch at Rio:
Michael Phelps, US: The most decorated Olympian ever, with 22 medals, will be competing in his fifth Games. Phelps won a remarkable eight golds in Beijing, but in his dotage he is only competing in three events at Rio, the 100m and 200m butterfly and 200m individual medley.
Katie Ledecky, US: The 19-year-old is the most dominant swimmer in the world right now, last year pulling off the remarkable feat of winning gold in the 200m, 400m, 800m and 1,500m freestyle at the World Championships. She has broken 11 world records and currently holds the 400m, 800m, and 1,500m freestyle records. She should leave Rio with multiple medals, most of them gold.
Chad le Clos, South Africa: After Le Clos pipped Phelps to gold in the 200m butterfly at London, his proud father gave a tearful poolside interview that went down in Olympic folklore. Le Cos is hoping that he can be centre of attention this time as he goes up against Phelps in the butterfly.
Katinka Hosszu, Hungary: The "Iron Lady" has yet to win an Olympic medal despite three previous attempts. A versatile swimmer who has won World Championship gold medals swimming backstroke, butterfly and freestyle and holds multiple world records will be favourite in the 400m and 200m medley events.
Yusra Mardini, Refugee Olympic Athletes: She won't win any medals at Rio but Mardini should get one of the biggest cheers of the Games when she competes in the 100m freestyle and butterfly. The 18-year-old was a promising swimmer in her native Syria, but when her home was destroyed in the civil war, she and her sister fled to Europe. While making the hazardous crossing to Greece, their refugee boat began to sink. Mardini, her sister and two other swimmers jumped overboard and pushed the stricken boat for three hours until they reached Lesbos.
When is the swimming on?
Swimming dominates the first week of the Games, with athletics taking over for the second week. Events begin just after 5pm UK time on Saturday 6 August, with the men's 400m medley heats. The first final, again the 400m medley, is just after 2am the next day.
There are four finals in the early hours of every morning from Sunday 7 August to Sunday 14 August.
The men's 100m breaststroke final featuring Peaty will be at 2.53am on Monday 8 August. Phelps and Le Clos will do battle in the 200m butterfly final at 2.28am on Wednesday 9 August. The men and women's 50m freestyle finals are in the early hours of Saturday 13 August and Sunday 14 August.
Events finish with the men and women's 4x100m medley relays on Sunday morning.
For those who prefer open-water swimming, the women's 10km marathon begins at 1pm on 15 August, with the men's event a day later.
