Forget walking on water. What if you could do yoga on the water’s surface, like a jellyfish riding the gentle waves in downward dog or child’s pose.

That’s basically the idea behind the Floating Fitness class at the Annenberg Community Beach House. It’s a full-body workout combining yoga and Pilates moves with gentle high-intensity interval training bodyweight exercises — all performed on floating yoga mats in a swimming pool.

The inflatable hardshell BOGAFiT mat that’s used — or “floating training platform,” as the class refers to it — looks like a wide paddleboard with a slightly raised yoga mat on its surface. It’s anchored to the pool walls with bungee cords on either end, so that the mat floats in the middle of the pool but doesn’t flip over. Participants can then get a high-intensity, low-impact workout that’s easy on the joints and requires extra balance, firing up the core. The workout builds strength and flexibility while improving balance and coordination, said instructor Leah Gutentag, who’s been a lifeguard and swim instructor for the city of Santa Monica for about 12 years.

“Being on the mat, on the water, it’s a unique experience,” Gutentag said. “It’s that balance challenge. No matter your workout experience — whether you go to Pilates once a week or once a year — all of those movements change on the water. Your body physically adapts, and your brain mentally adapts. You use stabilizing muscles in your feet you don’t normally use, you feel your core engaged.”

It’s worth noting that the Annenberg Community Beach House pool is directly across from the beach. You can’t exactly see the ocean while in the pool, but you feel its presence. I took the class on an early Saturday morning (it has since moved to Wednesday evenings). Warming up, we stretched out on our mats in a supine position, staring up at the sky and breathing deeply. Heavy seaside fog settled above us, and the air smelled salty. As the ocean breeze kicked up, the palms rustled around us.

It was utterly serene.

Until it was not.

“Keep that left elbow tucked into that right knee as we lift our left leg, then lower it,” Gutentag coached. “Now open from our crunch, and then crunch it back over. Lift, lower! Uncrunch, cross it back up! We’re here for four, for three, for two and one.”

Participants perform planks during Floating Fitness.

(Alisha Jucevic / For The Times)

The position was easy enough — I’d done it countless times on dry land. But even the simplest moves were noticeably harder on an unstable surface. I felt the effort in my abs for days afterward.

Vibe: The more than century-old pool at the Annenberg Community Beach House was once part of the seaside mansion that William Randolph Hearst built for his mistress, actress Marion Davies. It’s beautifully preserved and feels luxurious to workout in, as if you’re on a “wellness vacation” at a resort. The class is held when the pool is closed to the public, and with just a handful of participants the day I attended, the experience also felt exclusive. Instructor Gutentag has been teaching Floating Fitness at ACBH for more than a year now, and she led the group with authority and warmth, offering adjustments for those who needed it. Remarkably, during the hourlong class, only one person fell into the pool, sparking festive cheers among participants. (The water is a balmy 87 degrees, so no one suffered!)

Effort: Don’t expect an aerobic workout. But this class is tricky — the effort sneaks up on you. At first, the yoga and breathwork were easy. But as the class progressed, Gutentag introduced Pilates-style “pulsing,” which was more challenging. We performed classic moves: squats, crunches, high and low planks and bird dogs, among them. The instability of the water shined a light on areas of my body that were weaker than others. A spinal twist to the right, for instance, while doing a “thread the needle” pose, was far more difficult for me than it would be on land. Double heel raises, which are a breeze on land, were nearly impossible on the wobbly mat. I welcomed the challenge and plan to attend the class again to master the moves.

Zoe Krut, left, and Shayna Simmer make waves with their boards during Floating Fitness.

(Alisha Jucevic / For The Times)

X factor: There are plenty of low-impact, aqua workouts in Los Angeles. But they’re largely performed in the pool, using water as resistance. (Conversely, I also attended a paddleboard workout on dry land once.) Floating Fitness at ACBH allows you to do a mix of traditional yoga, Pilates and HIIT exercises as you would on a floor mat, but with the added instability of water — “safe instability,” as the class calls it. And in the refreshing atmosphere of a seaside pool. It’s the best of both worlds.

“This class for anyone who wants to be on the water doing something different,” Gutentag said. “It’s a fun way to keep your body moving.”