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The types of effluent discharged by wood-processing industries and their effects on the benthic environment are described. A brief summary of the results of the Lochs Linnhe-Eil survey 1964-70 is given. Populations of the molluscs Corbula , Thyasira and Myrtea have increased in most areas, and appear to be favoured by a moderate increase in the organic input to the system. Corbula dominates in the shallower polyhaline areas, and Myrtea in the deeper mixoeuhaline areas. On sediments with a high natural leaf litter content a low diversity fauna occurs, dominated by the annelids Cirriformia , Peloscolex , Capitella and Staurocephalus , and the crustacean Idotea . The predominance of this kind of fauna has increased in its area of occurrence in recent years. Comparisons of these faunal distributions and changes with those found in surveys in other marine areas affected by wood-processing wastes and other types of organic effluents show considerable similarities in the faunal changes occurring under increased organic loading. The utility of ‘indicator’ species in the assessment of organic pollution is briefly discussed. The need for detailed information on the ecological and physiological reasons underlying the varied faunal successions which occur under conditions of pollutional stress is emphasized.