Forty years after the release of their “Yellow Submarine” album, the Beatles are headed for another sub-sea adventure. The Fab Four — or at least divers costumed as the quartet — will take center stage Saturday, July 11, during the Lower Keys’ 25th annual Underwater Music Festival.

Musicians take center stage at the annual Underwater Music Festival -- this year to include an oddly familiar Fab Foursome.

Divers portraying “Ringo Starfish,” “John Lemon-shark,” “Paul McCarpney” and “George Herringson” are planning to rock the waters of the continental United States’ only living coral barrier reef during the offbeat event.

While the Beatles might not be the authentic originals, the event itself is authentic to the core — and it draws as many as 600 divers and snorkelers each year.

The submerged songfest is set for 10 a.m. to 2 p.m. at Looe Key Reef, part of the Florida Keys National Marine Sanctuary south of Big Pine Key. It celebrates the colorful marine life that thrives in the Keys’ unique coral reef ecosystem, and encourages environmentally responsible diving practices that protect the ecosystem.

Participating divers can even spot friendly mermaids at the Lower Keys' Underwater Music Festival. (Photo by Bill Keogh/Florida Keys News Bureau)

During the festival, finned fans can watch the Beatles pretenders “perform” beneath the sea accompanied by backup singer “Mako Ono”  — and they might even glimpse a replica yellow submarine saluting the album’s 1969 release.

The fish-friendly festival is staged by popular local radio station WWUS 104.1 FM, with the station’s musical selections piped underwater via special speakers suspended beneath boats at the reef.

 So what does music sound like underwater?

“It has a very ethereal sound — it seems to come from all directions,” advises festival coordinator and WWUS radio veteran Bill Becker. “The reason is that sound travels five times faster in water than in air, so it reaches both of your ears almost instantaneously, which gives it a very much of a surrounding sound.”

Each year the playlist includes ocean-themed ditties like Jimmy Buffett’s “Fins,” the unfortunately unforgettable theme from “Gilligan’s Island,” authentic humpback whale song and, of course, the Beatles’ “Octopus’s Garden” and “Yellow Submarine.”

Backup singer "Mako Ono" might wield this clambourine sculpted by Lower Keys artist August Powers.

Underwater musicians also jam on aquatic instruments sculpted by Keys artist August Powers. Blending elements of sea creatures and actual instruments, Powers’ creations include a trom-bonefish, manta-lin, drumfish and a clambourine.

(Note to readers: no, the puns won’t stop any time soon.)

Does seeing the Beatles in Lower Keys waters sound a little “fishy”? Well, they’re not the only unusual denizens of the deep that have appeared at the wacky festival. In recent years, participants have spotted a longhaired harp-wielding mermaid, several snorkeling Elvis look-alikes playing underwater guitar, diving diva “Britney Spearfish” and even, prior to the 2008 presidential election, “Barackuda Obama” and “John McClam.”

Get ready to rock the reef at the 25th annual Lower Keys Underwater Music Festival. Event founder Bill Becker can be glimpsed here waving the American flag. (Photo by Bill Keogh/Florida Keys News Bureau)

The Underwater Music Festival offers a one-of-a-kind opportunity for divers and snorkelers — but equally important is its ongoing focus on coral reef preservation. Each year, the musical broadcast features diver awareness tips on enjoying the ocean while minimizing impact on the reef environment — and that’s worth promoting, as the Beatles might say, “Eight Days a Week.”

Want to dive into the 25th annual Underwater Music Festival? Look for a Lower Keys dive charter at www.fla-keys.com or www.lowerkeyschamber.com.