CBSE Class 10 Science 2017 · Paper 531/3 · Question 6

Causes (any two): (i) Towns and cities along the river pour their garbage and largely untreated sewage (human excreta) into it. (ii) Industries discharge their chemical effluents into the river. (Human activities such as bathing, washing clothes and immersing ashes or unburnt corpses also pollute it.) Harm to health: sewage brings disease-causing microorganisms into the water (the presence of coliform bacteria shows this), so people who drink the water or bathe in it can suffer from water-borne diseases such as cholera, typhoid, diarrhoea and jaundice. The toxic chemicals in industrial effluents can poison the people who use the water; they kill fish, and some of them build up in the fish that people eat.