my dad has arthritis and was told swim or use exercise bike. He was told that it had to be the crawl he did to offer any help. He did not properly know how to do that and managed to get lessons from the lady who teaches my little nephew - he had two 45 minute lessons and really felt much more confident just after the first one. Your local pool would either offer instruction of recommend someone I am sure? Another alternative would just be holding a float and kicking your legs like you would do with the crawl - at least until you are stronger. Only problem with swimming, I am always starving afterwards(probably something to do with getting chips on the way home when I was younger). So have some healthy snacks ready. Also probably best not to put off the dieting but maybe not think of it as a diet, just cut down. Often even our portion sizes are the cause of weight increase - just reduce them a bit. Good luck!