Four-time Rio gold medalist Katie Ledecky is among Olympic swim stars entered in Mesa as USA Swimming re-sets for 2020.

Michael Phelps was retired when USA Swimming first brought one of its major professional meets to Mesa in 2013.

Now, starting a second Olympic quadrennium with Mesa continuing as part of the Arena Pro Series, Phelps is living in metro Phoenix and retired again, this time he swears for good after adding six more medals (five gold) at the Rio Olympics. His final Olympic scorecard – 28 medals, 23 gold.

“The greatest swimmer in the history of our sport is a big one to fill,” said Frank Busch, going into his final summer as USA Swimming national team director before retiring in September. “Our goal is to try and figure out how to do it by committee. We had one of the best Olympics we’ve ever had (in Rio) particularly for first-time Olympians. That is very promising, but you can’t base anything on past performance. It’s all about what’s next.”

In the short run, what’s next is the World Aquatics Championships, July 14-30 in Budapest. The new big-picture goal is the 2020 Tokyo Olympics, which could include 10 more medal events for 44 total if the International Olympic Committee approves a proposal by the international swimming federation (FINA).

The U.S. won 33 swimming medals (16 gold) in Rio, its most since the 2000 Olympics.

Busch said that this year “from a structure standpoint might be the most important when putting in the approach to make 2020 better than 2016. That’s what we’re doing right now.” Advancing pro swimming is first on that agenda, and Mesa is central each year as the first major outdoor long course meet.

“It draws us into the season right away,” said Busch, who coached at Arizona from 1989-2011 with men’s and women’s teams sweeping 2008 NCAA titles. It was Busch, after joining USA Swimming, who pushed for an Arena Pro Series meet in Mesa and who played a role in Bob Bowman leaving North Baltimore Aquatic Club to coach at Arizona State. Bowman was U.S. Olympic men’s coach in Rio, a role he could potentially have again in Tokyo.

This year in Mesa, Busch is as much a focal point for the meet as the 500-swimmer field that includes four-time Rio gold medalist Katie Ledecky and more than 20 U.S. Olympians.

Ledecky, 20, just completed her freshman season at Stanford, winning three individual titles and swimming on two American record-setting relays in leading the Cardinal to a dominant win at the NCAA championships. She is Honda Award winner for women’s swimming and a finalist for Collegiate Woman Athlete of the Year.

This will be Ledecky’s fifth consecutive Mesa appearance. She has 13 first-place finishes at Skyline Aquatic Center at distances from 200- to 1,500-meter.

Others entered this week include U.S. Rio medalists Simone Manuel, Nathan Adrian, Josh Prenot, Chase Kalisz, Conor Dwyer, Anthony Ervin and Katie Meili as well as 2012 Olympians Matt Grevers of Tucson and Breeja Larson of Mesa and local high-school stars Taylor Ruck (a two-time Canadian relay medalist in Rio) and Ryan Hoffer.

Three-time defending series champion Dwyer is returning to competition for the first time since Rio. Kalisz trained for Rio with Bowman at ASU and after earning a silver medal in the 400-meter IM returned to Georgia for his final college season, winning the NCAA 400-yard IM for a third time.

Grevers, 32, opted to continue in competitive swimming at least for one more year after the heartbreak of a third-place finish at the 2016 U.S. Olympic Trials, preventing him from defending his Olympic 100 backstroke title in Rio.

Larson, who turns 25 on Sunday, also is sticking with the sport for the time being. She is a four-time breaststroke champion in her hometown meet.

Ruck, 16, finished fourth to eighth in four finals last week at the Canadian World Championships Trials, failing to qualify for Budapest and instead will swim at the World Junior Championships, Aug. 23-30 in Indianapolis.

Arena Pro Swim Mesa

When: Thursday-Saturday.

Where: Skyline Aquatic Center, 845 S. Crismon Rd., Mesa.

TV: NBC Sports Network, 10:30 p.m. Friday and Saturday (tape delay).

Times: 9 a.m. preliminaries, 5 p.m. finals.

Information: usaswimming.org.