From the very wide range of activities dealt with in this review, dealing with a great variety of problems in many countries, it is clear that the period under review has been one marked by a great upsurge of interest, and by remarkable progress in a hitherto much-neglected aspect of running water contamination. In fact this period of intense interest in the special problems of the macroinvertebrate fauna (as distinct from those of freshwater fish) of streams and rivers, may indeed encompass a peak period of study which is perhaps already on the decline. This is perhaps inevitable. Problems of particular interest or importance, or ones for which unusually ample funds are available for research, attract and encourage the most competent researchers, whose interest and scientific dedication in turn engenders further enthusiasm (Brown, 1973). This leads to the build up of multidisciplinary teams capable of making massive contributions to knowledge during their tenure.

This has certainly been the case with some of the major projects examined in detail in this review. For example, the OCP (Onchocerciasis Control Programme) inaugurated in 1974 on a 20-year basis has produced team work of the highest productivity during its first 10 years. Key research workers tend to move to other fields, or to retire; the teams become disbanded and funds for research tend to dwindle. It is difficult to visualise that the same intense research effort on the impact of Simulium control measures on non-target macroinvertebrates, and on stream ecosystems, will continue at the same high pitch for the next 10 years of the programme.