What’s it like to swim into the world’s weirdest underwater orgy?

This female cuttlefish is having none of it, however, and expertly slips out of the lothario’s grasp and darts off in a flash of purple tentacles. But before I chalk it up as a win for the sisterhood, I spot two other males glowing turquoise in pursuit. I start to follow them, but get distracted by another male putting on a spectacular display of colors for a female, who looks sufficiently impressed. Just a few feet away, another pair of soft-bodied cephalopods are already getting down to business, totally unbothered by the human voyeur—me—floating less than two meters away.

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Nearly 400 kilometers (250 miles) north of Adelaide, near the top of the big V-shape missing from South Australia, the tiny Upper Spencer Gulf Marine Park provides the perfect conditions for the world’s only known mass spawning of giant cuttlefish.

Each May, some 200,000 of these highly intelligent critters converge here, about 30 kilometers (18 miles) north of the industrial town of Whyalla, to literally mate themselves to death, with all but a robust few disintegrating by the end of August, before the next generation has hatched. With all the action going down just off the rocky shore, anyone with a snorkel and a good wetsuit can enjoy a front row seat.

Cuttlefish researcher Dr. Alexandra Schnell discovered that females can physically ‘swipe left’ by displaying a white stripe along the side of their body to indicate when they’re not interested.

Due to their expressive behaviour, active sex life and short life spans, Australian giant cuttlefish are known as the ‘rock stars of the sea’, says Charter as he talks us through the mating rituals to look out for during our snorkel off Stony Point, a popular immersion spot.

Despite the surplus of males during the breeding season, the females are a picky bunch. In 2015, cuttlefish researcher Dr. Alexandra Schnell discovered that females can physically ‘swipe left’ by displaying a white stripe along the side of their body to indicate when they’re not interested. Some males inevitably don’t get the message, but at least the ladyfolk have a chance to make their intentions clear.

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Bobbing above the frenzy in my wetsuit, I’m so entranced by the sex fest—which was filmed in this very spot for David Attenborough’s Blue Planet II—that I forget how cold it is for a minute. The water needs to be around 57 degrees Fahrenheit for the females to lay, and after about 30 minutes paddling around in water a few degrees cooler than that, I’m spent.

“Males are even partial to a bit of cross-dressing,” he says. “You’ll see smaller males change their color to mimic the females so they can move in on a mate without the big boys noticing.”

Swimming back to shore, I observe a lifeless pink tentacle drift past—a glimpse of the fate that awaits this mob at the end of the season, if predators don’t beat them to it. I’m more worried about the great white variety—which are not uncommon in these waters—snacking on me, but Charter assures me he’s only ever spotted sea lions and dolphins while snorkeling here.

Charter expects David Attenborough’s ‘Blue Planet II’—which was viewed by so many people in China upon its October 2017 release that it slowed the nation’s internet—will inspire more travelers to make the trip this season.

Disgorging myself from my wetsuit, I marvel at how this incredible phenomenon, which has been observed here for around 20 years, has remained relatively unknown—even within Australia—until now. The remoteness and relative lack of attractions in the area (unless you fancy a tour of Whyalla’s old steelworks) are no doubt contributing factors.

But Stony Point might not stay this sleepy for long. Combined with the increase in cuttlefish numbers over the last couple of years, which makes braving the icy water a much more worthwhile endeavour, Charter expects Blue Planet II—which was viewed by so many people in China upon its October 2017 release that it slowed the nation’s internet—will inspire more intrepid travelers to make the trip this season.

Following a trial run last winter, July will see Adelaide-based operator PureSA launch overnight tours from the capital during the season’s peak, including a cuttlefish info session and guided snorkel with Charter, who is also an underwater photographer, and Program Manager at Experiencing Marine Sanctuaries, a Whyalla not-for-profit that aims to foster appreciation and conservation of the marine environment.

If you’ve got your own wheels, Whyalla Diving Services can kit you out with snorkeling or scuba diving gear, and arrange a guide if you need one. During the past year, a shelter, picnic tables and change rooms have been installed at Stony Point, which is handy if you’re planning to make a day of it out here. You can even make a night of it, with a handful of designated camping spots nearby (though you’ll have to head into town for food).

Despite switching my wetsuit for three layers of warm clothing, I still can’t feel all of my toes by the time we make a pit stop in the Clare Valley, just over halfway back to Adelaide, for a restorative Shiraz. Any by the way, if there’s one thing you need after dropping in on 200,000 cephalopods literally shagging themselves to death, it’s a restorative Shiraz. Perhaps two.

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