The way TS4 combines (and sometimes doesn't combine) activities into skills can be quite strange more often than not. On the one hand, there's Piano and Pipe Organ, which are treated as two different skills despite being basically the same instrument, except that the organ has a little something extra down there. On the other hand, we have woodworking and electrical engineering lumped together under Handiness, and (the worst offender for me personally) Logic, which covers several natural sciences... (and chess.)
Like others in this thread, I'm not sure if there's really enough to swimming to make it a separate skill, unless it was combined with something else like diving, but Island Living unfortunately missed that opportunity. Ice skating and rollerblading being a hidden skill and otherwise contributing to Fitness is annoying, though. I've never been into sports, but became a queen on the ice rink from the moment I first skated on one, so to me, those are two entirely unrelated skills. :D
