Still, the main swimming events should gain the most attention, especially with local standout Mireia Belmonte of Spain a multi-medal threat. Even if Phelps, who had his breakout meet in Barcelona in 2003 by winning four golds as an 18-year-old, isn't around anymore.

Phelps retired after last year's London Olympics as the most decorated Olympian of all-time, with 22 medals. He competed at his first worlds in 2001 in Fukuoka, Japan, breaking the world record in the 200-meter butterfly to become - at 15 years and 9 months - the youngest man ever to set a swimming world mark.

"For us, Phelps is an icon. He's the greatest Olympic athlete of all-time and I think it will be 100 years before someone matches his medals record," Marculescu said.

Olympic and world champion Sun Yang prepares for his upcoming 400m and 1,500m freestyle events in the World Swimming Championships in Barcelona, Spain, on July 23. [Photo/Xinhua] More photos on Sun Yang

So what about those reports that Phelps is considering returning for the 2016 Rio de Janeiro Olympics?

"It's his decision, not ours. He worked very hard over the years and I think he wanted to do some other things in life. I hear he is playing golf. But I also think that maybe he is missing his love, which is swimming," Marculescu said.

Other swimming story lines should be Australia's attempt to bounce back from its poor showing in London, when it won only one gold for its worst showing in 20 years. Australia head coach Leigh Nugent resigned in March.

Aussie sprinter James Magnussen will be defending his gold from the 2011 worlds in the 100 freestyle after settling for silver at the Olympics.

Meanwhile, France will want to confirm itself after finishing third in the London medals table behind the United States and China with Yannick Agnel, Florent Manaudou and Camille Muffat leading the way.

However, many medalists choose to train less the year after the Olympics.

"It always happens like that but then you see them bounce back again," Marculescu said.

The post-Olympic year syndrome could be one of the reasons why FINA decided to include high diving before even holding a World Cup event in the discipline, which is based on the Red Bull Cliff Diving series.

Swimming officials said they need innovation after watching the ancient sport of wrestling lose its spot on the Olympic program.

About 20 men are expected to compete in high diving but only six women. Women just competed for the first time in the Red Bull series earlier this month in Malcesine, Italy.

"It's very small because it's the beginning," Marculescu said. "But you have to start from somewhere."