I don't understand as to why light enters the water only through the yellow region. I understand that beyond the yellow region, the reflected bottom of the pool will be seen (green rays in figure below), but wouldn't it be a dim (less bright) compared to the light entering the water from the air (red rays in figure below) and reaching the fish? I assume a infinite or very large pond here (not an aquarium where light may enter from the sides too) so that the reflected light from the bottom of the pond is quite dim. Hence the fish must see the outside world superimposed with a dim reflection of the bottom of the pond. Where am I going wrong?

Thanks in advance for your reply and for your great post.