Dear Andy and Blue;-
> (Is Blue your real name?)
  I once read that the waters of the Ohio river, from the time they leave
Pittsburg, to the time they reach the Gulf, have been used over 19 times by
drinking, washing, flushing, and lawn watering. Does that sound right?
   Art

Sounds likely. Of course, the major uses of water are not very dirty. A
great deal is used for irrigation and for cooling industrial processes, for
instance. And it's good to remember that a water molecule is not dirtied by
any of the uses that it is put to.

In the late nineteenth century, landfills were often placed along riverbanks
and lakeshores, or trash was simply dumped into the water. This in addition
to sewage and discharge from industry. Populations of mollusks (and their
fish hosts) plummeted in many watercourses, and riverview apartments were
not popular.

Today, it's hard to believe that American rivers once supported a thriving
pearl-button industry as well as fisheries. All these things were present
not so very long ago -- you can still read about them in old magazines.

Have you ever tried photographing a scene from the same vantage point as an
old picture? It's called 'rephotography' and it can be fascinating. To the
teachers out there, who are looking for children's projects: I'd recommend
starting out with a picture that includes an easily recognized landmark such
as a bridge.

Andrew K. Rindsberg
Geological Survey of Alabama