I was a bit surprised about the efficiency of swimming as well. Obviously, water has much higher viscosity than air. But, on the other side, pretty much 100% of

I was a bit surprised about the efficiency of swimming as well. Obviously, water has much higher viscosity than air. But, on the other side, pretty much 100% of the muscle movement can be translated into forward movement and no need to expend energy moving up and down against gravity. Also, a fish can glide a bit, unlike a walking animal (less than a bird, obviously). Also the fastest fish (sailfish) is similar to the fastest land animal (cheetah) at somewhere around 110kmh.