Explanation

Organic matter (organic wastes) contains a number of pathogens, secondary pollutants, pesticides, etc. Biological oxygen demand becomes high and therefore, the dissolved oxygen reduced. Hence, planktons, Mollusca and fishes will be eliminated due to reduced dissolved oxygen and presence of secondary pollutant. Some species like annelid wormTubifex and some insect larvae (Chironomus) tolerate pollution.