Scuba Diving is a skill in The Sims 3: Island Paradise. Sims learn this skill by snorkeling in the ocean. As they advance this skill, they can start scuba diving in diving areas.
Snorkeling
Sims can go far out in the ocean and snorkel to improve their Scuba Diving skill. Snorkeling or taking Scuba Diving classes is the only way to improve the skill enough to be able to actually dive. Snorkeling may turn up small collectibles such as shells.
Dive Lots
There are 4 diving areas in Isla Paradiso. Each diving area has Scuba Diving skill requirement. One of the diving areas is first available to Sims when they reach the Scuba Diving skill level 2. Once the Sim boats or swims to above the dive lot, Sims with sufficient Scuba Diving skill can scuba dive underwater. The lots are decorated with many rocks, coral and other objects. There are also gems and fish on the lot that can be caught, underwater caves to explore, and the treasure to discover. Mermaids can also often be seen and socialized with at the various dive lots. Other worlds will not be updated to have diving areas, but advanced players can add them on their own.
Air
While scuba diving, Sims only have a certain amount of air before they must return to the surface. The amount of air the Sim has depends on their Scuba Diving level. The air Sims have left is shown by a moodlet. Once the first moodlet that they got when they started diving is gone, they will get a negative moodlet that shows that they are having trouble breathing and should return to the surface.