In industrial areas the waste water from the high concentration of population and heavy industry can cause overload of relatively small rivers. Uniform emission standards for the discharges are inappropriate even in these areas as variations in river flows would make a uniform standard too relaxed or too stringent, according to circumstances, at different points. The problem of fixing river quality standards which would allow fish to repopulate the industrial rivers in Yorkshire and then of applying them to produce appropriate standards for effluents has been examined by a group from the Yorkshire Water Authority. Provisional river water quality standards are recommended in different forms and the bases for these are discussed and comparisons made with the field measurements of river water qualities and the presence of fish. The standards are suggested as mean or median or 95 percentiles as appropriate and also in some cases as maxima which should not recur more often than a critical period if fisheries are to be self sustaining. Methods for applying them to the many effluent discharges in the industrial areas of Yorkshire are also discussed.

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