Swim, swam, swum

Has anyone addressed this before? The past participle of "swim" is "swum." "Swam" is the simple past. You can say, "I swam three times last week" or "I have swum in that pool many times," but you can never say "I have swam ..." It's simply not correct English. Sorry to be persnickety, but as a former book editor, it drives me crazy every time I see it, and I see it increasingly more often now that I spend so much time here.:nono: