I rendered an animation and everything's great - sky and trees and grass wiggle in the wind... but the water doesn't ripple.

I applied the "Tropical Water" from the Animated category and darkened the water to look like a muddy pond. Other than that, I don't believe I changed anything.

Any ideas what's wrong? The animation is 30 seconds, and the whole point of the animation is to watch my building wiggle in the beautiful pond reflections.