Summary: Salmo gairdneri, Cyprincs carpio, Poecilia reticdata, Leuciscus idus melanotus, Asellus aquaticus, Ankistrodesmus falcatus and Monoraphidium grifjithii were exposed t o four growth regulating herbicides, four photosynthesis toxicants, lindane, an anionactive tenside, KCN and Na,[Cu(CN),] in standardized toxicity tests. The biochemical degradability of the substances was tested with activated sludge. In order t o test the possible effects in waters there should be used Salmo for the oligosaprobic zone. Poecilia as well as Ankistrodesmus and Monoraphidiurn provide reliable estimations for @-mesosaprobic waters. With respect to the longer-term permission of plant protection products, besides Salmo there can be recommended also Leuciscus.