If you have a strength of 4 and an agility of 6, you can swim 5 meters without have to roll as a Simple Action.
If you had two passes, you could swim once each pass for a total of 10 meters that Combat Turn.
So you could swim and also perform a second simple action (not swimming) that pass, such as fire a weapon or recklessly cast a spell.
If you needed to swim faster, you could spend a Simple Action to swim 5 meters, then spend another simple action to 'sprint', rolling Swimming + Strength and adding the amount of hits in meters to your distance.
Mind you, this isn't decided yet, they may decide something different, bit at least this makes more sense.