Funny. There are three things that I feel could have helped blending his figure better in the scene. Faking the shape of the legs underwater, rather than their reflections, even if the water surface is obviously quite reflective at this angle.Applying a bit of toning to the whole image and angling the shadow on his body a bit more towards the viewer. Faking big waves rather than big sprays of water would have been more convincing as well.
Love the old man peacefully contemplating the big boy in transit :D