You need to buy an air tank (capsule) from the bait shop, and it gives you oxygen for maybe 3 mins or something. Just like the jetpack. So you don't drown.
You dive to swim in depth of the sea or any water in the active city to find pearls, treasure and etc. There can be "Jewelry shop" added like Ikevoodoo suggested so that you sell your findings to the shop. Selling high value stuff like treasures, old coins and expensive pearls is illegal, so you'll become wanted for it.
You'll get wanted levels when you deliver the fundings.
Why?
- some people like to spend time alone and just earn or do some activity
- It's another new way to commit minor crimes
Now instead of typing -1, give some ideas and use your brain.