I know this for sure. Swimming will be done during indoc. I don't know if there is a certain distance/period of time to tread water/test that they give there, but I would suggest getting in good physical shape for swimming. Try to learn all the strokes(just in case). I would suggest to do about 500-1500 yards(like 2-3 times a week) a workout if you weren't in a swim team before.