San Andreas Swimming
Swimming in San Andreas with CJ is a whole new feature in the game's franchise. In previous Grand Theft Auto titles, once you entered water, vehicle or without, you were dead. In San Andreas, you can actually get out of your car in the middle of the water and start swimming to shore!
Swimming isn't the only thing that you can do in the water. You can also dive deep in the water to hide from the police, gangs, and even hide yourself on covert missions. When you dive, you will notice that you have a "lung" meter. This "meter" measures how long you can stay under the water. Over time, this meter will increase, giving you the ability to dive for a longer period of time.
There are two things you can do to increase your lung capacity. The first is simply to keep swimming around underwater, and a after a few minutes or so, you'll start to see your lung capacity increase (obviously you'll need to surface for air when your breath runs low).
The second way is to find the oysters hidden underwater. After finding all of these your lung capacity will most likely be full, and your sex appeal will also have increased.