You were against the light. So the head is in shade. When light reflects from the waters and you are photographing either turtle or tiger in water, please look at the bright and dark areas in the image. The digital camera sensor doesn't have the dynamic range to see both dark and bright areas unlike our eyes. So When you are composing, it is better to avoid the extremes (bright white and deep blacks) in one frame.

It would have been good if you could have photographed this scene with the sun on your back.

Cheers,
Sabyasachi