[Publius6961]

I am not a enviro-wacko, but I have heard stories about the silt build up and the pollution of the Mississippi lately...

Ummm... yes.
If it's a river, two things are certain: erosion and siltation.

For about 6 Billion years, now.

[conserv13]

I know that, duh...

There are ways that human activity can affect that though, both positive and negative.

[UCANSEE2]

Rivers are just the trains the dirt rides on.