Help with a character controller

Hi,

I am pretty new to Unity scripting and have been using the First Person Controller prefab. I am now working on a world where most of it is underwater and I need my character to be able to swim around. I am a bit lost looking through the CharacterMotor.js code and was hoping someone could give me some tips on what I need to modify to allow the character to move up or down and not stay grounded. Or should I disable this script when underwater and use a different one? Thanks.