How do you guys get those smooth, cinematic underwater tracking shots? My footage is always shaky.

I've been trying to step up my underwater video game with my GoPro HERO12. I've got the settings dialed in (4K, 60fps, 8:7 aspect ratio), but my footage still looks amateurish because it's so shaky.

Whenever I try to follow a turtle or a ray, my kicking motion makes the camera bob up and down. I see these amazing, smooth tracking shots on YouTube that look like they were shot on a drone. Are people using massive gimbals, or is there a specific swimming technique I'm missing? Any advice for getting smoother footage?