Swimmers compete during the men's 10-kilometer swimming marathon at the 2012 Summer Olympics.

Athletes compete during the men's 10-kilometer swimming marathon at the 2012 Summer Olympics.

South Africa's Hercules Prinsloo (front) drinks during the men's 10km open water swimming marathon at the London 2012 Olympic Games at Hyde Park in London.

Gold medalist Eva Risztov of Hungary, left, and silver medalist Haley Anderson of the United States race to the finish in the women's 10-kilometer marathon swimming competition at Hyde Park at the 2012 Summer Olympics, Thursday, Aug. 9, 2012, in London.

Hungary's Eva Risztov (C) poses with her gold medal flanked by silver medalist Haley Anderson of the United States (l) and bronze medalist Italy's Martina Grimaldi (R) after winning the women's 10km open water swimming marathon at the London 2012 Olympic Games on August 9, 2012 in London.

Germany's Angela Maurer, front, and other athletes dive into the Serpentine at Hyde Park as they compete in the women's marathon swimming competition at the 2012 Summer Olympics Thursday, Aug. 9, 2012, in London.

South Africa's Jessica Roux competes in the women's 10-kilometer marathon swimming competition at Hyde Park at the 2012 Summer Olympics, Thursday, Aug. 9, 2012, in London.

Swimmers compete in the women's 10 km marathon during the swimming competition at the London 2012 Olympic Games on August 9, 2012 in London.

US swimmers (from left) Brendan Hansen, Matt Grevers, Nathan Adrian and Michael Phelps celebrate winning the men's 4x100-meter medley relay on Saturday. The gold gave Phelps 18 to cap his legendary career, and 22 medals overall.

VIDEO: Amy Van Dyken recaps Saturday's final day of swimming in the pool.

Michael Phelps reacts after he competed in the men's 4x100 medley relay final. Phelps brought his Olympic swimming career to a close in style, winning a record 18th gold medal as the United States stormed to victory.

VIDEO: Phelps' crowning achievement stirs fans' reaction.

Michael Phelps' mom Debbie Phelps reacts next to sisters Hilary (left) and Whitney.

VIDEO: Amy Van Dyken recaps the final day of swimming.

Michael Phelps surged through the water in the fly, handing off a lead of about a quarter of a second to Nathan Adrian for the freesytle anchor. The Americans won going away in 3 minutes, 29.35 seconds, just off their own Olympic record from Beijing. Japan held on for silver in 3:31.26, with Australia taking the bronze in 3:31.68.

VIDEO: Phelps' big finish draws big reaction from fans.

Gold medalists (from left) Missy Franklin, Rebecca Soni, Dana Vollmer and Allison Schmitt of the United States celebrate on the podium after winning the women's 4x100-meter medley relay final. The US set a world record in the win.

MORE: Who's leading the Olympic medal count?

Australia's Leisel Jones swims in the women's 4x100-meter medley relay final. The Aussies finished second behind the United States.

MORE: See all of the gold medals won by Americans so far.

Competitors prepare for the start of the women's 4x100 medley relay.

VIDEO: Amy Van Dyken recaps Saturday's final day of swimming in the pool.

MORE: Olympic athletes are becoming stars in London. Find out what makes them tick.

China's Sun Yang is overcome by emotion after his gold-medal win in the men's 1,500-meter freestyle final Saturday.

MORE: They said what?! Keep up with all the juicy athlete tweets.

China's Sun Yang (center) beats out Tunisia's Oussama Mellouli (right), Canada's Ryan Cochrane (left) and the rest of the field in the 1,500 freestyle.

MORE: Fans show off their colorful Olympic pride.

Therese Alshammar of Sweden blows water from her mouth ahead of the women's 50-meter freestyle final.

MORE: Look back at the top moments of an incredible opening ceremony.

Silver medalist Aliaksandra Herasimenia of the Netherlands congratulates countrywoman Ranomi Kromowidjojo on winning the women's 50 freestyle on Saturday.

MORE: Fans show off their colorful Olympic pride.

The Netherlands' Ranomi Kromowidjojo (center) touches the wall ahead of Belarus' Aliaksandra Herasimenia (right) and compatriot Marleen Veldhuis to win the women's 50-meter freestyle swimming final.

MORE: Full Olympics results.

From left, South Africa's Chad le Clos, United States' Michael Phelps and Russia's Evegnu Korotyshkin pose on the podium after medaling in the men's 100-meter butterfly swimming final on Friday.

Michael Phelps competes in the men's 100-meter butterfly final on Day 7, where he picked up his 17th gold medal, and his 21st overall.

Michael Phelps acknowledges the audience after he won the gold in the men's 100-meter butterfly swimming final on Friday.

MORE: They said what?! Keep up with all the juicy athlete tweets.

Team USA's Missy Franklin starts in the women's 200-meter backstroke final on Friday. Franklin won her third gold medal in the event, and her fourth overall, setting a world record in the process.

Missy Franklin, on her way to winning more gold, this time in the women's 200-meter backstroke final.

Missy Franklin, left, and teammate Elizabeth Beisel congratulate each other after winning gold and bronze, respectively, in the women's 200-meter backstroke final on Friday.

Yang Sun of China dives into the water at the start of the men's 1,500-meter freestyle heat 4 on Day 7.

MORE: Olympic athletes are becoming stars in London. Find out what makes them tick.

Swimmers take the start of the men's 4 x 100-meter medley relay heats during Friday action in London.

MORE: They said what?! Keep up with all the juicy athlete tweets.

Mexico's Arturo Perez Vertti Ferrer competes in a 1500-meter freestyle swimming heat.

A general view of the athletes including Chang Gao (CHN), lane 4, in the starting blocks for the women's 4x1000m medley relay heats.

Team USA's Katie Ledecky reacts after her gold-medal win in the women's 800-meter freestyle swimming final on Friday.

The United States' Tyler Clary celebrates winning gold in the men's 200-meter backstroke Thursday, Aug. 2.

MORE: Who's leading the Olympic medal count?

Fans of Ryan Lochte hold up placards bearing a photograph of him on Thursday, Aug. 2

MORE: Fans show off their colorful Olympic pride.

Netherlands' Ranomi Kromowidjojo competes in the women's 100-meter freestyle final Thursday, Aug. 2.

United States' Missy Franklin competes in a women's 200-meter backstroke heat Thursday, Aug. 2. Franklin, a gold-medal winnner earlier in the London Games, reached the final but finished fifth.

Daryna Zevina of Ukraine competes in the women's 200-meter backstroke heats Thursday, Aug. 2.

Elizabeth Beisel of the United States celebrates after being pleased with her swim in a semifinal of the women's 200 backstroke.

Michael Phelps competes in the men's 100-meter butterfly heats Thursday, Aug. 2.

France's Laure Manaudou (right) competes in the women's 200-meter backstroke heats Thursday, Aug. 2.

Michael Phelps (nearest lane) oand Ryan Lochte (center) compete in the men's 200-meter IM on Thursday, Aug. 2. Phelps won gold, Lochte silver.

Denmark's Lotte Friis competes in the women's 800-meter freestyle heats on Thursday, Aug. 2.

France's Laure Manaudou competes in the women's 200-meter backstroke heats Thursday, Aug. 2. The photo was taken with a robotic camera above the pool.

Nathan Adrian of the United States celebrates after he won the Final of the Men's 100m Freestyle on Day 5 of the London 2012 Olympic Games at the Aquatics Centre on August 1, 2012 in London, England

WATCH: Recapping Wednesday in the pool.

Bronze medalist Brent Hayden of Canada, gold medalist Nathan Adrian of the United States and silver medalist James "The Missle" Magnussen of Australia pose with their medals during the medal cermony for the Men's 100m Freestyle on Day 5 of the London 2012 Olympic Games at the Aquatics Centre on August 1, 2012 in London, England.

MORE: See what the Duchess of Cambridge, Kate Middleton, has been up to at the Olympics.

US swimmer Rebecca Soni swims a world record in the women's 200m breaststroke semifinals swimming event at the London 2012 Olympic Games on August 1, 2012 in London.

MORE: Fans show off their colorful Olympic pride.

US swimmer Rebecca Soni celebrates after breaking the world record the women's 200m breaststroke semifinals swimming event at the London 2012 Olympic Games on August 1, 2012 in London.

MORE: Look back at the top moments of an incredible opening ceremony.

Frmo left: Americans Shannon Vreeland, Dana Vollmer and Missy Franklin celebrate after the women's 4x200m freestyle relay final swimming event at the London 2012 Olympic Games on August 1, 2012 in London.

MORE: See all the hottest action from beach volleyball.

PICTURE TAKEN WITH A ROBOTIC CAMERA:  US swimmer Dana Vollmer (left) competes in the women's 4x200m freestyle relay final swimming event at the London 2012 Olympic Games on August 1, 2012 in London.

MORE: Olympic athletes are becoming stars in London. Find out what makes them tick.

Japan's Ryosuke Irie competes in the men's 200m backstroke heat on Aug. 1. Ryosuke finished fourth.

Hungary's Daniel Gyurta celebrates his gold medal win in the men's 200-meter breaststroke swimming final at the Aquatics Centre on Wednesday.

Nathan Adrian of the United States celebrates his win — by the smallest of margins — in the men's 100m freestyle event on Wednesday. Adrian's time of 47.52 seconds was 0.01 seconds ahead of world champion James "The Missile" Magnussen of Australia.

Britain's Michael Jamieson swims to a silver medal in the men's 200m breaststroke final on Aug. 1. It took a world record-breaking swim from Hungary's Daniel Gyurta to beat Jamieson.

Swimmers start in a men's 200-meter backstroke swimming heat at the Aquatics Centre on Wednesday.

Japan's Ryosuke Irie, center, competes in a men's 200-meter backstroke Wednesday.

MORE: Full Olympics results.

Austria's Markus Rogan is disqualified from a men's 200-meter individual medley swimming semifinal Wednesday. Judges said Rogan's turn maneuver at the wall was illegal, but even without the disqualification, he was not among the event's top eight finishers.

United States' Ryan Lochte arrives for a men's 200-meter individual medley semifinal at the Aquatics Centre on Wednesday. Lochte won his heat, placing first overall in 1:56.13, and will compete on Thursday in the final against teammate Michael Phelps.

USA's Ryan Lochte competes in a men's 200-meter backstroke semifinal Wednesday at the Aquatics Centre. Lochte won his heat in 1:55.40, placing second overall and will swim in the final Thursday evening.

United States' Ryan Lochte starts in a men's 200-meter individual medley semifinal on Wednesday. He won the heat and will compete in the final on Thursday.

Ryan Lochte of the United States competes in heat 5 of the men's 200m backstroke Wednesday. Lochte won this heat and will swim in the final on Thursday, trying to win the 10th medal of his Olympic career.

Debbie Phelps, mother of Michael Phelps, watches the men's 4x200m freestyle relay final on Tuesday. The US team took first as Michael Phelps won an Olympic-record 19th medal, breaking the old mark of Soviet gymnast Larisa Latynina (1956-'64). Phelps' career totals include 15 golds, two silvers and two bronze medals.

MORE: They said what?! Keep up with all the juicy athlete tweets.

Michael Phelps fails to beat South Africa's Chad le Clos (green cap) in the men's 200-meter butterfly final on Tuesday. The silver medal was Phelps' 18th career Olympic medal — he would win his record-breaking 19th later in the day when the US 4x200 relay team took the gold.

MORE: Who's leading the Olympic medal count?

American Allison Schmitt reacts after winning gold in the women's 200-meter freestyle on Tuesday. It's the first career gold medal for Schmitt, who set an Olympic record with a time of 1 minute, 53.61 seconds.

MORE: See the best images from Tuesday. View photos.

(Front to back) Japan's Takeshi Matsuda, South Africa's Chad le Clos and Michael Phelps compete in the men's 200-meter butterfly on Tuesday. Le Clos finished first, followed by Phelps and Matsuda.

MORE: Olympic athletes are becoming stars in London. Find out what makes them tick.

Michael Phelps finishes the final leg of the United States' winning 4x200 freestyle team on Tuesday. Teammates (left to right) Conor Dwyer, Ryan Lochte and Ricky Berens react to their gold-medal win.

MORE: Look back at the top moments of an incredible opening ceremony.

China's Ye Shiwe (right) is embraced by Australia's Alicia Coutts after winning gold in the women's 200-meter individual medley on Tuesday.

MORE: Who's leading the Olympic medal count?

South Africa's Chad le Clos reacts as he wins gold in the 200 butterfly on Tuesday. Michael Phelps finished second.

Ricky Berens (left) and Ryan Lochte congratulate teammate Michael Phelps, still in the water after swimming the final leg of the gold-medal winning 4x200 freestyle relay team on Tuesday.

Ryan Lochte, Conor Dwyer, Ricky Berens and Michael Phelps show off their gold during the medal ceremony for the American's first-place showing in the men's 4x200 freestyle relay on Tuesday.

Netherland's Lennart Stekelenburg comes up for air in men's 200m breaststroke.

Japan's Kosuke Kitajima competes in the men's 200m breaststroke.

China's Jiao Liuyang makes a move in a women's 200-meter butterfly swimming heat.

Swimmers make a dash in the men's 200m breaststroke.

Spain's Mireia Belmonte Garcia keeps perfect form in the women's 200m butterfly heats.

Canada's Scott Dickens shows off his endurance in the men's 200m breaststroke heat.

United States' gold medalist Missy Franklin enjoys the medal ceremony with Japan's silver medalist Aya Terakawa after the women's 200-meter freestyle on Monday.

American Missy Franklin starts the women's 100-meter backstroke final at the Aquatics Centre in the Olympic Park on Monday.

From left, Irie Ryosuke (Japan), Matt Grevers and Nick Thoman (Team USA) pose with their medals after the men's 100m backstroke finals.

Matt Grevers, left, reacts after winning the gold medal with teammate Nick Thoman, who won the silver in the men's 100m backstroke finals.

Camille Lacourt of France, Matt Grevers of the United States and Liam Tancock of Great Britain compete in the final of the men's 100-meter backstroke on Day 3.

MORE: Olympic athletes are becoming stars in London. Find out what makes them tick.

From left, Satomi Suzuki (Japan), Ruta Meilutyte (Lithuania) and Rebecca Soni (Team USA) pose with their medals after the women's 100m breaststroke finals.

Ruta Meilutyte of Lithuania celebrates after winning the final of the women's 100m breaststroke on Day 3.

MORE: They said what?! Keep up with all the juicy athlete tweets.

Yannick Agnel of France celebrates after winning the final of the men's 200-meter freestyle on Day 3.

Yannick Agnel of France realizes he just won gold.

Competitors dive into the pool in the second semifinal heat of women's 200-meter freestyle on Day 3.

Michael Phelps, after the second semifinal heat of the men's 200-meter butterfly on Day 3.

MORE: Full Olympics results.

Michael Phelps, center, competes in a men's 200-meter butterfly swimming semifinal.

Michael Phelps, left, starts in a men's 200-meter butterfly swimming heat at the Aquatics Centre in the Olympic Park on Monday. Phelps was fifth in the heats to advance to the semis, where he won his race and earned the No. 4 seeding for the Tuesday final.

Taiwan's Hsu Chi-Chieh competes in a men's 200 swimming heat.

Italy's Federica Pellegrini swims out of the pool after a women's 200-meter freestyle heat on Monday, July 30.

France's Camille Muffat competes in a women's 200-meter freestyle heat on Monday, July 30.

Michael Phelps competes in the men's 200-meter butterfly heats on Monday, July 30.

Michael Phelps competes in heat 5 of the men's 200-meter butterfly on Day 3.

MORE: Who's leading the Olympic medal count?

Michael Phelps of the United States reacts after he competed in Heat 5 of the men's 200-meter butterfly prelims on Monday, July 30. Phelps qualified for the final with the fifth-fastest time: 1 minute, 55.53 seconds.

Team USA's Nathan Adrian, Michael Phelps and Cullen Jones look on during the men's  4 x 100m freestyle relay Sunday in London. The Americans won silver.

From left, Australia's Christian Sprenger (silver), South Africa's Cameron van der Burgh (gold), and United States' Brendan Hansen (bronze) celebrate their medals in the men's 100-meter breaststroke swimming final on Sunday.

Team USA's Dana Vollmer, foreground, learns of her gold-medal win in the 100-meter butterfly swimming final Sunday.

France's Camille Muffat, right, touches the wall to finish ahead of Team USA's Allison Schmitt, winning gold in the women's 400-meter freestyle swimming final Sunday.

Americans Ricky Berens, top, and Ryan Lochte, center, and China's Sun Yang compete in the men's 200-meter freestyle swimming qualifying Sunday at the Aquatics Centre in the Olympic Park. Yang won the heat in 1:46.24 and was the top qualifier for the final just ahead of Lochte (1:46.45), coming off his win in the 400 IM on Saturday.

Hong Kong's Au Hoi Shun starts in a women's 100-meter backstroke heat at the Aquatics Centre in the Olympic Park. She placed last in her heat.