When permits for the discharge of chemicals into a waterway are issued, they are issued in terms of the number of pounds of each chemical that can be discharged into the waterway per day. These figures, calculated separately for each chemical for which a permit is issued, are based on an estimate of the effect of the dilution of the chemical by the amount of water flowing through the waterway. The waterway is ttherefore protected against being adversely affected by chemicals discharged under the permits. The argument depends on the assumption that ['the danger of chemical pollution of waterways is to be evaluated in terms of human health only and not in terms of the health of both human beings and wildlife', 'there is a swift flow of water in the waterway that ensures rapid dispersion of chemicals discharged', 'relatively harmless chemicals do not interact with each other in the water to form harmful compounds', 'there are no chemicals for which discharge into waterways is entirely prohibited']