This is a video from the Noboribetsu Marine Park in Japan of a seal that has a circular ring to swim through that’s above the waterline, which works on the same principle (atmospheric pressure) as those floating pond bubbles that fish can swim up into. Per Youtube commenter agerven on how it was made:

They fill the circle first while it is completely under water. Then they put it upright while maintaining the ends under water. So there still is no air, only water in the circle. Since the atmospheric pressure on the water in the pool compensates for the weight of the water in the circle you get a stable configuration.

Yeah that made no sense so let’s just assume science has been thrown out the window and this aquarium has a water witch or wizard on the staff. Remember: the simplest, most logical answer is usually the right one.

Keep going for the video, as well as a bonus one of a seal appearing to nap in the ring.