Use the W, A, S, D keys to move in water
Press and hold Shift to swim faster
Press Space to dive underwater
Press Ctrl to rise toward the surface
Use the mouse to change direction
Move toward the shore or a boat to get out of the water
If you are in story mode, switch to a character with better stamina if needed
If you are in a vehicle, exit it before swimming
If you fall into deep water, keep moving to avoid drowning