Can one mourning a parent swim after the shiva period/ during the 30 day or 12 month?
During shloshim the avel should not go swimming if it is for pleasure purposes, however if it is for medical reasons, of because he is a lifeguard etc. then it is permitted.
During the 12 months the avel may go swimming.
Kol Bo pg 356, Kitzur Shulchan Aruch 209-7, Nitei Gavriel Aveilus vol. 2 8-3, Ohel Yackov Aveilus 4- 48,49.