The report of the Council on Environmental Quality (1970) repeatedly stresses the need for the development of predictive, simulative, and managerial capabilities to combat air and water pollution. The last capability depends on the first two . For example, the effects of every waste put into a river will have to be predicted if the river is to be managed as a system wherein industrial use of the water does not preclude other uses such as recreation and municipal water supply . In addition, the effects of alternative river management schemes should be simulated first, and then carefully monitored when the schemes are put into practice . In short, the capability of successfully managing a river for many uses depends on the capability to predict effects . The capability of predicting biological effects is particularly important, because desirable functions of aquatic ecosystems, such as waste assimilation and game fish production, depend on living organisms . The standard fish bioassay, which uses death as a response, enables one to predict the toxicity of a particular waste to fish . One limitation of the standard bioassay is that it uses a grab sample which represents the quality of the waste at one point in time . The water used to make the dilutions is also taken at one point in time . At the actual industrial site, the quality of the waste and the river water vary through time. A composite waste sample partially overcomes this limitation, but may mask variations that are biologically important . For example, the toxicity of zinc to fish is affected by the calcium concentration and temperature of the water