When the first act of "Das Rheingold" — the first of four operas in Richard Wagner's "Der Ring des Nibelungen" cycle — unfolds at McCaw Hall a year from now (Aug. 4, 2013, to be exact), the sight of three mermaids, the Rhinemaidens, swimming, diving and singing will likely stir audiences as it has in previous productions of Seattle Opera's "Ring."

It takes a near-mythical effort to organize such a feat, aerial mermaids included, and already at work on it is Thea Railey, Seattle Opera's assistant stage manager, technical aerial consultant and standby Rhinemaiden.

The mermaids will be played by Jennifer Zetlan, Cecelia Hall and Renee Tatum, each of whom will simulate watery movement while suspended three stories above the stage. The trio will execute acrobatic choreography yet manage, through a specially designed harness, to sing.

That's a full 20 minutes of pure exertion for the vocalists (who are also aloft in "Götterdämmerung"). But the colorful staging requires rigorous preparation, by the production's technical crew (including two linesmen per singer), the stage management team, fitness experts and others.

Railey is a key figure in the mix, as she knows what it's like to entertain from dizzying heights plus oversee a thousand details during Seattle Opera performances.

Railey, 35, made her stage debut for the opera in 2007, playing Young Iphigénie in "Iphigénie en Tauride." Her silent character was rescued from certain death by Lara Paxton's goddess Diane, who swooped down and flew off with her.

It was all in a day's work for Railey, a Colorado native who holds a music degree, studied acting at New York's The Neighborhood Playhouse School of the Theatre, and took up aerialism (performing in the air from a hoop, length of silk, etc.) for Off-Broadway shows.

"As my desire to be on stage in more traditional ways faded, aerial work came in," says Railey. "Height adds a new dimension to the work.

"When you're dancing, you can do amazing things, but adding aerial to choreography adds imagination and visual effect."

Railey also pursued stage management, which she calls "a good fit for someone with organizational tendencies." In 2006, she went to work both for Seattle Opera and New York City Opera, until Seattle became home.

Railey joined local group The Aerialistas — Paxton's popular, sexy troupe with a burlesque edge — and the related Aerial Suites. She has appeared five times in the Triple Door's holiday revue "Land of the Sweets: The Burlesque Nutcracker."

But it's at Seattle Opera that Rainey finds all her skill sets welcome. An assistant stage manager on current production, "Turandot," she is also now working with Zetlan, Hall and Tatum on their in-flight coordination for "Ring."

"The hardest part of training is just getting used to the harness," Railey says. "It takes a lot of core strength to support your body so you can sing, flip around and pull yourself horizontal. Singers really have to start getting in shape now so they have strength and endurance."

Railey is also understudying all three performers, requiring her to know their music, lyrics and choreography in case she has to fill in (which happened in 2009).

"I'll do aerial cover, but an offstage singer will cover the vocal while I mouth the words," Railey says. "A tricky piece is that at 5 feet 2 inches, I am quite small. It takes time for the linesmen to adjust to my lighter weight and quicker movements. It takes finesse to make sure I and the other girls turn just the right amount. Too little means flying sideways, and too much risks us spinning upstage and twisting the wires."

Tom Keogh: tomwkeogh@gmail.com

This story was corrected on Friday, Aug. 3, 2012. In an earlier version, Lara Paxton was incorrectly identified on first reference.