Apple stated Ultra's dive app is for dives down to 50'. There are no time limits or decompression stops for dives within 50 feet from sea level; especially if it's just the one dive.

The Huish Oceanic Plus app has finally arrived for the Apple Watch Ultra, allowing recreational divers to use the rugged smartwatch as a wrist-worn dive computer. The app will cost $9.99 monthly ...

And Series 10 gains features from the Ultra 2 – the water depth gauge and water temperature sensor. Like with Series 9 and Ultra 2, the Blood Oxygen feature is not available in the US for Series 10.

Apple says you might want to send your Apple Watch Ultra for a Depth and Water Seal Test if: You’d like to check the functionality of the depth gauge in your Apple Watch Ultra. You might have caused ...

Apple Watch Ultra snorkeling mode vs. the Depth app. The Oceanic Plus app also has a free snorkeling mode which I tested alongside the built-in Depth app at my apartment complex pool.