SOUTHPORT, Australia — At this week’s Pan Pacific Championships, Claire Donahue’s job is not on the line, but her paycheck is.

The American swimmer owns the 13th-fastest time in the world in the 100-meter butterfly, the event in which she finished seventh at the London Olympics. To retain her post-NCAA stipend of $3,250 a month, which has been her primary source of income since she graduated from Western Kentucky in 2011, Donahue must be in the top 12.

The source of Donahue’s sustenance is the Athlete Partnership Agreement, introduced by USA Swimming in 2011 to help postcollegiate athletes stay afloat financially as they continue to pursue their Olympic dreams.

Donahue, 25, is one of 13 women on the U.S. squad here who have exhausted their college eligibility. The number is higher on the men’s side, where the average age of the 30-member squad is 24.

The post-collegiate swimmers’ circumstances are as different as their strokes. In contrast with Donahue, who says she has no idea how she will pay her bills without the stipend, there is Michael Phelps, who is financially set and is searching for projects to occupy his time once he retires for real.

Phelps, 29, and his longtime coach, Bob Bowman, recently entered into a partnership with the equipment manufacturer Aqua Sphere to develop swim gear and apparel, including a racing suit Phelps said he planned to unveil next year. He said of the opportunity, “Hopefully, this is forever.”

Anthony Ervin, the only American besides Phelps at this meet who raced in Australia at the 2000 Olympics, lives in Northern California’s East Bay, where his stipend does not stretch far. Ervin, 33, who trains at California Aquatics, gets by but said: “I couldn’t have a family. There’s really no stability.”

In addition to the USA Swimming stipend, Ervin, third in the world in the 50 freestyle, has an apparel contract. In the winter he competes on the World Cup circuit in Europe and assorted other dash-for-cash events. The money can be excellent — an event in Perth is sponsored by an energy company and has a $250,000 purse — but it can be costly to a swimmer’s training and fitness to devote a large chunk of the winter to racing.

One of Ervin’s main rivals on the sprinting circuit is his Cal Aquatics teammate Tom Shields. This summer, Shields said, he was on the verge of permanently shelving his Olympic aspirations. Then he touched out Phelps in the 100-meter butterfly and won the 200 butterfly at the recent USA Swimming long-course nationals to make his first U.S. national “A” team.

Shields, 23, who is engaged to be married, said: “I was thinking, I need to get this together or I need to stop swimming. I need to give it everything I have, and if I fall short, that’s it.”

Matt Grevers, who won three medals, including the 100 backstroke gold, at the London Games, said he had also thought about calling it quits. Married last year to Annie Chandler, a former national team swimmer, Grevers, 29, is motivated to achieve long-term financial security, but with swimming as his only job, it is hard.

“That’s the one thing that will probably get me to retire more than anything else,” Grevers said. “That nagging feeling that, ‘All right, I need to secure an income for my family, for my family’s future.’ ”

With the performance bonus money he received in 2012 from sponsors and the U.S. Olympic Committee, Grevers bought two houses in Tucson, Arizona, his longtime base. He started Grevers Inc. for tax purposes, named his wife the chief operating officer and set a salary for himself for serving as the chief executive. The couple lives comfortably now. But what about 10 or 20 years down the road?

“Because once we’re done it’s not like we made enough money to retire,” Grevers said. “We have to find a job, and for all these years while other people were climbing those career ladders, we were swimming. So we’re behind.”

That work gap can be narrowed, said David Marsh, who coaches 17 post-collegians at SwimMAC Carolina in Charlotte, North Carolina. Marsh, a member of the U.S. Pan Pacific coaching staff, prods his older athletes to advance their outside interests as their focus remains on moving up the swimming chain.

“You can be networking, collecting business cards and following up on those business cards,” Marsh said. “I tell them to think about what you want to be doing beyond swimming and build relationships.”

It worked for Micah Lawrence, 24, a world-class breaststroker and budding artist who procured a paid internship with a Charlotte-based designer wear company through an introduction brokered by the swim coach at Queens University of Charlotte. Lawrence, who competed at Auburn, is finishing her degree in graphic design at Queens in Charlotte while training with Marsh.

“It’s just a great opportunity for me because I get to have that internship while I’m also still swimming,” Lawrence said, adding: “You definitely have to find a way to sustain yourself.”