Do you know I can't swin , however by splashing around I can do about 20 length - not fast though
The only thing I do is some walking and exercise bike. 3 years ago I could not walk but I had an operation which meant I could not drive so it forced me to walk. Now if i don't walk for a day or two, I get withdraw sympstoms and hav eto go out walking even if it means going to the end of the gate and come back.
Good luck with swimming and do not worry about the weight, just relax and have variet and you lose without even realising.