Blimey Kahleesi I hardly know where to start in praising water-based exercise for fatties.
OK let's start by saying that, in the water, a 20 stone woman feels 10 stone. Is that enough to tempt you?
Because your entire weight is supported by the water, by your own buoyancy, in fact, you can for example kick your legs about like a mad thing and it takes very little effort. I cannot even lift my legs when I am on dry land. (For example when attempting to climb onto b/f's motorbike, I literally cannot lift my leg up high enough to get it over the saddle.) But in the water, I can lift my legs as though they are weightless, and touch (kick) the wall level with my shoulders.
I bought a Speedo Aquabeat (google it) and this has revolutionised my in-pool time. Basically, I'm having my own private disco, in the water. I dance, crazy-dance, under the water, to the beat of my favourite old 1970s dance music, and I forget I am fat, forget I am in water, forget everything : all that matters is moving to the music.
TRY IT!