Read this speech [PDF] by Mehan (ex-EPA). It’s deep and thorough:

For too long water quality management has been characterized by compartmentalization and the creation of artificial boundaries among and between various aspects of what should be a unified approach to water quality in terms of the chemical, physical and biological integrity of the nation’s waters. It has tolerated, even encouraged a bifurcated approach, allowing unnecessary polarities to dominate policy and practice: water quality versus quantity; land versus water; surface water versus groundwater; point versus nonpoint sources; energy versus water; and supply-side versus demand-side management.

I particularly liked his reference for Chicago being the biggest polluter on the Mississippi:

Footnote 35: I have made this assertion in the presence of officials with the Chicago Water Reclamation District several times, without eliciting any protests, just smiles.

Now, if you want to know how to model and manage a watershed, then you will want to get some good, multi-disciplinary advice, and that’s why you should read this paper [pdf], which will help you…

…gain an understanding of how various human activities affect watershed processes, and in turn how the variable nature of the hydrologic cycle affects humans’ well-being, is essential for policy makers and watershed managers.

Next problem, please?