Water and reflections (FS9)

This is a question for the folks that really understand which texture files do what...

Right now my water (rivers) look very good at a somewhat flat angle of viewing.  But if I look more straight down, they look black.  I would like to try and have them look more muddy brown; or at least something more organic than black.  Should I be playing with the "sky_" series of textures, or the "env_" series?  Or something else?  Or maybe there is a relationship between the different textures?

Any enlightenment would be appreciated!  Thanks.

Ron