Please forgive me is this is a stupid question!

A few days ago, while sitting by the river during a tea break, I noticed something interesting that got me thinking. It had become quite an overcast day, with very little definition in the clouds, but some sunlight shining through.

I noticed however that the reflection of the sky on the river showed quite considerably more detail and interest in the clouds. I was wondering why this should be and how I might recreate the effect on film.

I'm guessing it is has something to do with the polarizing effect the water has on the reflected light, in which case would a polarizing filter have a smiler effect? Or maybe the water only reflects some of the light, and absorbs the rest, acting like a coloured filter?

Then again, I was nearing the end of a 12 hour shift, so I could have been seeing things!