Biochemical ecology is here presented only in the context of water pollution. This is not to minimize the importance of land animals and plants in their environment or the significance of air pollution as it relates to ecology. It merely indicates that water pollution is a problem of sufficiently broad magnitude to warrant consideration by itself. Water pollution is a problem which requires the attention of a variety of disciplines. The presentation tends therefore to follow the problem ap proach, as do most interdisciplinary topics. An appreciation of various viewpoints is needed among chemists, ecologists, economists, engineers, lawyers, limnologists, managers, microbiologists, and politicians, whose communications are often "hung up" in each other's jargon. Perhaps the presentation is too elementary at times. This was done in an attempt to bridge the diverse backgrounds of those concerned with the subject. It is hoped that engineers, economists, biologists, public servants, and others will gain a greater appreciation of the interrelationship of gross observations and biological events that occur at the cellular and molecular level. Lack of such understanding is, to a large extent, the reason for our present environmental condition. At other times the presentation is perhaps too technical. This was done on the assumption that some information on chemical details may not be readily available but is desirable for an "in depth" appreciation of the biochemical events encountered in water pollu tion."