Not Platte

Why the hell are all these rivers brown?
Do the fish, perhaps, prefer it so?
Or are they, like the landscape, beaten down
By wind and ice and unforgiving snow
Until the very essence of their flow
Is murked by the effluence of the land?
I'm sure that it must help the crops to grow
For there they flourish, as if by command,
But can it really, on the other hand,
Be best to have the water so opaque,
The color of an almost-wettened sand
Or peanut butter malted chocolate shake?
I do not know, but as it passes through
It bothers me it isn't very blue.