It’s sink or swim — in fabulous costumes — when you dive in with Seattle Mermaids

I DIDN’T THINK I had fantasies of being a mermaid, but as soon as I saw the Seattle Mermaids in their shiny, colorful tails, I wished I had a full outfit, complete with a seashell crown.

Fortunately, mermaid J. von Stratton came prepared, and loaned me a tie-dyed tail and shiny fish-scale top.

And I thought I was at the Bellevue Aquatic Center to swim.

We did that, too. The Seattle Mermaids don’t offer a formal mermaiding class. The mermaids I met learned to swim on their own, using a monofin. It’s basically free-diving with costumes, explained one mermaid, Essie. They perform sometimes, and they also gather to hang out together in “Mer World.”

After putting on their tails — a workout in itself — we sat at the edge of the deep end of the pool. Jump in, von Stratton encouraged.

I stared at the water. Having my feet bound together in the monofin made me nervous. I made myself get in.

I attempted to tread water with my hands, and used my feet to move my monofin forward and back, but I kept pulling my knees to my chest, a common mistake. I felt like I was going to sink. Mermaids told me to keep my hanging legs down and my hips under my chest: Use your fin to keep yourself upright.

I struggled for a couple minutes, then gave in and grabbed the wall.

Swimming underwater is easier. Essie, who also free-dives, told me the best way to swim is with your arms straight, head down, rolling your body. Von Stratton handed me a pair of bedazzled goggles, and I went under.

It was mesmerizing. Mermaids swam about, looking graceful as they glided around at the bottom of the 13-foot deep end, their tails fanning out behind them. Sometimes they swam on their backs, faces up toward the top of the water. Some wore tails they bought; others made their own or added jewelry. They are mindful about using materials that are safe in pools.

Too soon, von Stratton suggested I try on the tie-dyed tail. I wasn’t sure I was ready, but apparently it was time. I shimmied it on, then got back in the pool.

Putting the tail on over my monofin gave me a boost of confidence. I went under, undulating in the body roll and remembering to stretch out my arms and look down. I was surprised at how deep I went with such a simple motion. It was easier with my legs encased in the tail. I also ran out of breath, and had to swim quickly to the surface. Essie took photos with an underwater camera; I looked like a real mermaid.

For the rest of the hour, the mermaids swam, took photos and chatted. Dedicated mermaids swim once or twice a week on their own, working on breath control. After seeing how they swim in the deep end, I can understand why.

Mermaiding uses your core and lower back to create the wave of your legs, torso and feet. I don’t swim regularly, and I was fully worn out after 45 minutes.

You can learn to mermaid on your own, though you should check to see whether your local pool allows it, and start in shallower water. I picked it up faster than I thought. And once you get into it, you might also see why mermaids love to do it together — they dress up, admire each other’s tails and swim. What’s not to love?