ABSTRACT
We have by now seen ample evidence that the levels of abundance and patterns of distribution of aquatic organisms may be affected by pollution of the water in which they live. Hellawell (1977, 1978) summarised diagrammatically the changes which may occur in a community subject to pollution (Figure 3.1). Which, if any, of these responses occur will depend upon the nature and severity of the pollution, and upon the relative susceptibility of the species within the community to specific kinds of environmental alteration. It follows that given suitable techniques of sampling and data analysis, monitoring of the biological characteristics of waters might indicate the occurrence of ecologically significant environmental changesincluding the incidence of pollution-which may otherwise be undetected.
