Weight / Fat loss

I agree with the thermal conductivity thing (people get hypothermic and die much quicker in cold water) but I don't know enough physics to dispute the idea about the calories. What I will suggest though is that at a high work rate, humans are producing a fuck load of heat, so exercising in water is 'maybe' more efficient since your body doesn't need to work so hard to cool down? Also, there's bouyancy in water, so you're moving but body weight is part suspended. So you're working to go forward but not support yourself, like say, running. Need a proper scientist to answer this. I hate swimming though, unless I'm chasing a can of beer down a river...