Women rule the 2013 pool, Phelps hints at return
A picture taken on August 4, 2012 shows US swimmer Michael Phelps diving as he competes at the London 2012 Olympic Games in London
The 28-year-old Phelps walked away from swimming after winning a record 18th gold medal at the London 2012 Olympics.
But having registered with the United States Anti-Doping Agency, Phelps will be eligible to compete at the US trials for the 2015 World Championships in Kazan, Russia, and has not ruled out a comeback ahead of the 2016 Rio de Janeiro Olympics.
"I don't know what's gonna happen in three years. I don't even know what is gonna happen tomorrow," said Phelps earlier this month when asked about a possible return.
"It's 'the million-dollar question'."
With Phelps missing from August's world championships, the ladies shone in Barcelona with US teenage star Missy Franklin, 18, winning six gold medals while Katie Ledecky, 16, won four golds and smashed both the 800m and 1500m freestyle records.
Ledecky shaved nearly six seconds off the 1500m record, then lowered the 800m mark, while Denmark's Rikke Moller Pedersen also set a new 200m breaststroke record.
Lithuania's 16-year-old star Ruta Meilutyte built on her 100m Olympic breaststroke triumph by winning the world gold over the same distance in Barcelona and also claimed the world records over 50m and 100m.
China's long-distance freestyle star Sun Yang was again in devastating form after winning the 400m and 1500m finals at London 2012, and won 400m, 800m and 1500m golds in the Barcelona pool.
But Sun, 22, fell offside with Chinese authorities last month when he was found to have driven without a licence after a white Porsche Cayenne he was driving was rear-ended by a bus in the eastern city of Hangzhou.
China's sports authorities have subsequently banned him indefinitely from competition after he was given seven days' detention and fined by police.
Sun's fellow Chinese star Ye Shiwen endured a tough 2013.
The 17-year-old later described her Barcelona form as a "nightmare" after the Olympic champion finished fourth in the 200m individual medley in Spain and seventh in the 400m race -- more than 10 seconds slower than her world record set in London.
Her poor form has been blamed on a growth spurt as she has put on weight since her London success.
There were no such problems for Hungary's Katinka Hosszu who won both the 200m and 400m medley world golds in Barcelona and scooped the World Cup title over the course of the season, claiming several short-course records in the process.
US star Lochte had an unfortunate end to the year as the five-time Olympic swimming champion finishes 2013 injured after an over-excited teenage fan knocked him over.
Lochte, who won three golds and a silver in Barcelona, suffered a torn knee ligament when the 29-year-old was knocked over in Florida when a female fan leapt at him.
South Africa's Chad le Clos, 21, flew the flag for the Rainbow Nation in 2013 adding the 200m butterfly world crown to his Olympic title and won the season's World Cup title, adding to his 2011 triumph.
Le Clos and compatriot Cameron van der Burgh picked up in Barcelona where they left off in London with Le Clos winning both the 100 and 200m butterfly golds, then picked up his first world short-course record in the 200m butterfly in Singapore in November.
Van der Burgh, the Olympic champion, finished second in the men's 100m breaststroke world final to Australia's Christian Sprenger, but struck gold in the 50m final with revenge over Sprenger.
After poor performances, by their own lofty standards, at both the 2012 Olympics and 2013 world championships, Australia have appointed highly-respected Dutchman Jacco Verhaeren as team head coach to help restore its reputation.
Both freestylers James Magnussen and Cate Campbell shone in the Barcelona pool with the pair winning their respective 100m finals after disappointment in London.