Did you do your squats today?

As you build up strength in your legs consider using some TRX straps and a door frame. You want to get more of your full body weight on your legs at some point. Also consider some knee braces even in the pool. You will build strength more effectively if your knees are bendin properly.

Also don't go down so far, ideally you want your thighs to be parallel with the ground, but if that is too far, don't go down so far. The idea is to use all the muscles in your legs, make sure to keep your heels planted and push down through your heels.