Swim speed multiplier.
Multiplier goes up to 1.49
Just call it one time, it is not required to be called once every tick. - Note copied from below native.
Note: At least the IDA method if you change the max float multiplier from 1.5 it will change it for both this and RUN_SPRINT below. I say 1.5 as the function blrs if what you input is greater than or equal to 1.5 hence why it's 1.49 max default.