Olympic swimming story lines

Michael Phelps is back for a sequel to his Olympic farewell.

This time, he insists, it really is goodbye.

After retiring and then un-retiring, Phelps will be in Rio as the first U.S. male swimmer to compete in five Olympics. He is already the most decorated athlete in the history of the games, with 18 golds and 22 medals overall, and at age 31 remains the biggest star in a sport that will also feature teen sensation Katie Ledecky and an increasingly diverse pool of potential champions from around the world.

Just don't expect another comeback.

"This is it," Phelps said. "No more."

Sure about that? "I'm done," he reiterated. "The body is done. This is my last one."

Here are some other things to watch at the swimming competition in Rio, which includes open water and the synchronized events:

Australia has traditionally been the second-strongest swimming nation behind the U.S., but the team from Down Under endured a dismal showing in 2012 with only one gold medal and no individual victories. Look for a big comeback in Rio. The Aussies returned to form at last year's world championships with seven golds and 16 medals overall. Sisters Cate and Bronte Campbell lead the way, along with Emily Seebohm and Mitch Larkin.

Missy Franklin was one of the big stars in London, winning four golds and a bronze while competing in seven events. The 21-year-old American will have a lot more free time on her hands this time after a disappointing performance at the U.S. trials. Franklin qualified for only two individual events and her relay duties will be limited to the 4x200 freestyle. It's a similar story for another U.S. great, Ryan Lochte. The 11-time Olympic medalist sustained a groin injury on the first day of the U.S. trials and managed to qualify for only one individual race — a far cry from the six events (four individual, two relays) he had in London.

For the second time in three Olympics, the schedule has been altered so the swimming events can be televised live in the U.S. during prime time. In Rio, the prelims have been moved back to 1 p.m. local time, while the finals won't begin until 10 p.m. — both about three hours later than most meets.

The 10-kilometer open water races, a part of the Olympics since 2008, will be held against the gorgeous backdrop of Copacabana. The state of the water is not so pretty. There are major health concerns after Brazilian officials failed to live up to their pledge to clean up an ocean contaminated with raw sewage and potentially dangerous bacteria.

Russia's the favorite in synchronized swimming and have not been beaten at the Olympics since 1996. But if Russia is ultimately banned from the games because of widespread doping, the podium might look much different this time around.