Chapter 1 covers the introduction and an overview. It indicates the ways in which aquatic ecosystems are valuable to mankind, and make a first pass at suggesting how these values might be assessed. In the next chapter we discuss a kind of quick and dirty alternate approach to valuation, the construction of a suite of indicator variables (SIV) that might be used to characterize the response of an aquatic ecosystem to reduced pollution or other disruption. Chapter 3 is about the dynamics of ecosystem recovery. Chapter 4 is an analysis of error propagation in measuring recovery. Chapters 2, 3 and 4 are primarily about the behavior of aquatic ecosystems, with no systematic discussion of economic valuation. In chapter 5 we begin this discussion. Chapter 6 covers the economic concept of benefit; Chapter 7 covers methods of benefit measurement; and Chapter 8 covers futher work.