A rigorous introduction to the development and use of mathematical models for in-stream water quality applications. Emphasis is on understanding models as tools: where they come from, what they do, and their strengths and limitations. The goal of the course is to help students become confident, wise users of models and modeling systems. Students write and use simple computer programs in exercises designed to illustrate various modeling concepts. Professional level modeling environments are introduced. Class focuses on fate and transport of constituents in streams and rivers, and includes an introduction to the use of water quality models in developing TMDLs. Contact instructor for prerequisites.