This new edition of a very successful standard reference is expanded and fully reworked. The book explains and quantifies the processes whereby streams cleanse themselves, reducing their pollutant load as a natural process. Mechanisms of purification in running waters have always been critical with regard to clearly identified pollution sources. This new edition explains the self-purifying function of streams and rivers in light of recent EPA rules on nonpoint pollutants and total maximum daily loads (TMDLs). It also covers basic concepts such as biological oxygen demand (BOD). Also new in this edition is an extended discussion of how streams originate and how they fit into the geomorphology of the earth and other water supply sources. Information is presented on aquatic life, including macroinvertebrates and their role as bioindicators of stream health. Chapter review tests and answers are included so that the readers can evaluate their mastery of the concepts presented. Stream Ecology and Self-Purification: An Introduction, 2nd Edition serves as a practical introduction to ecology combined with an explanation of how streams absorb and react to pollution. This text will prove valuable to water and wastewater plant operators, watershed managers, trainers, environmental students, water quality professionals, and will be an excellent preparation aid to wastewater/water operator licensing exams.