I think it would be better if it were a little lower perspective so it does not look like you are looking down on him. A bit more bottom below and fence to the side would provide more context. And a little less centred would improve as well.
Obviously if you could jump in the lake and get his face it would capture the emotion but many that's going to far
I agree with Scott's suggestions, except I wouldn't show the boys face and I personally think a centered crop would work well here. But I also think that it looks a bit overexposed. Maybe move the levels slider around a bit for a more pleasing look. Other than that, I think this is a pretty effective image.
