Why does the moon cast such a narrow path across water?

Question

As high as it is in the sky, why doesn't it cast a wider path (cause the whole river to glow)?

Answer 1

If you shine a torch/flashlight towards a mirror, why doesn't the whole mirror light up rather than you seeing and image of the torch? Same reasoning - reflection of something that is subtending a visual angle of about half a degree. In the case of a river, unless it's stagnant water and there's no wind, you'll get an image a little bigger than the moon because of the uneven reflecting surface of the water.