The significance of off-flavours in water and fisheries management is briefly discussed, as are guidelines for future research. In order to elucidate the sources and causes of off-flavours in natural waters, an integration of sensory, chemical and biological research is needed. Sensory characterization of off-flavours often involves taste and odour threshold measurements. Current techniques at water works are critically discussed. The need for a more comprehensive approach, where sensory response is related to stimulus intensity over a large range of magnitudes, is stressed. The use of consumer panels in sensory assessment of water quality is advocated. Sensory methods are useful screening methods. Chemical analyses should be related to the sensory characteristics of the compounds analyzed. Recent research on biogenic off-flavours in natural waters have indicated that they are more, complex than originally conceived. Criteria for establishing the odour production by organisms are presented. Compilations of scientifically proved taste and odour producing algae and micro-organisms may be useful, but more research is needed on the reasons for variability of their odour production. The development of relevant abatement techniques depends on a more complete understanding of the etiology of off-flavours in natural waters.