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The composition of the fish stock, food and 'macroparasites' were studied in eleven basins (22-100 m) of Lake Jyvasjarvi and North Paijanne in August-September 1976 . The fishing was done by means of a series of nets (meshes 15, 21 and 35 mm) laid on the bottom overnight . No fish were found in the two northernmost basins owing to bad oxygen conditions caused by waste waters . Smelt and burbot were the most abundant fish in the catches in other basins but the vendace was rare . Relict crustaceans and some `deep water' copepods (e .g . Heterocope borealis) played an important role in the food of fish in all basins .Parasites spreading via relict crustaceans were abundant in smelt and burbot, but absent in vendace and ruffe . The most common parasite in smelt was Cystidicola farionis, in burbot Echinorhynchus borealis, in ruffe Triaenophorus nodulosus and in vendace the gill parasite Ergasilus sieboldi. Females of a relatively rare copepod Salmincola lotae were found in the oral cavity of five burbot (at depths of 50 and 100 m) .

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The annual reproductive success of Coregonus albula and C . lavaretus in some polluted and clean areas of the central parts of L. Paijanne was estimated in 1981-90 on the basis of occurrence of larvae in shore seine and seine net samples after the ice melted. In polluted areas (0-5 km from Kaipola paper mill) larvae of coregonids were found only occasionally. In semipolluted areas (5-15 km from the paper mill) the densities of larvae were usually less than 0.1 ind m-2. In 'clean' areas the mean densities of larvae ranged from 0.45 to 5.34 inds m-2. A relatively high reproductive success of vendace was observed in 1984-85, moderate success in 1982-83 and low success in 1986-90. The larvae of whitefish were scarce in both polluted and semipolluted areas and their density ranged from 0.01 to 0.15 ind m P 2 in clean shores. The highest density was observed in 1989. In spite of the improvement of the quality of water in the area in the 1980s, the reproductive success of coregonids is still low in a great part of the basin which may depend on adverse oxygen conditions of the hypolimnion and sediment and the toxic effects of the effluents.