If used for drinking, polluted water may transmit various intestinal infections such as typhoid, cholera, dysentery and certain other diseases, e.g., jaundice and viral diseases. Public health authorities are now becoming greatly concerned about various toxic chemical pollutants found in waters, viz.

, nitrates, selenium, cadmium, mercury, chlorinated hydrocarbons and biocides. Health hazards caused by the use of polluted and naturally toxic seafood (e.g., shell fish, clams, other invertebrates, etc.) are now well-known. Besides drinking, other uses which may affect human health are swimming, bathing, use of water for agriculture, fisheries and in food industries, etc.

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Pollution of freshwaters results largely from the case of waste disposal there. Many of our lakes are becoming increasingly murky, smelly and choked with excessive growths of algae. Most of the rivers have become darkened with sewage, chemicals, oil, industrial effluents and undesirable foreign and extra­neous matter. In India, the river Damodar is one of the most heavily polluted rivers. It has been heavily abused as a convenient dumping ground for wastes and effluents of all kinds, including agricultural, industrial and domestic. Many parts of the river do not seem to have any dissolved oxygen and no wonder they fail to support the growth of any desirable aquatic organisms. Only such organisms as bloodworms, sludge worms, bloodsuckers and certain other undesirable animals, pathogenic bacteria and pests are found.

River Mini-Mahi in Baroda is another heavily polluted river which is loaded with a variety of industrial and petrochemical wastes. Recent surveys of several Indian rivers have also revealed severe pollution. It is believed that at present, rivers are the most severely afflicted systems (by pollution), followed by estuaries, lakes, and oceans in declining order. Occasionally, certain water bodies become so heavily polluted with oil that they have been seen to literally catch fire. In 1968, the Ganges caught fire near Monghyr (Bihar) because of the oily effluent discharged from the Barauni Oil Refinery. Large scale discharge of waste water containing arsenic and ammonia resulted in mass killing of fishes in an estuary near Goa a few years ago.

Water pollution is most often caused by uncontrolled rejection of wastes (Table 8.6). Although water pollution can be caused by the presence of any extraneous, undesirable matter, the following are some of the more important primary sources of pollution. During monsoons, thousands of tons of topsoil in India erodes and washes off. The land area prone to flooding has doubled from 200 million hectares to 40 million hectares since 1973.

Current estimates indicate that about 75% of India’s available water is polluted. The Ganga, which drains a quarter of the country’s land area, is now one of our most polluted rivers, sharing this dubious distinction with the Damodar (Bihar, W. Bengal), the Mini-Mahi (Gujarat) and the Yamuna (U.P.). Waste water, sewage and effluents from industrial plants of all types are being dumped into these waters, gradually converting them into open sewers.

Cherrapunji was once covered with lush green dense forests and was the wettest spot on earth; it is now degraded to the state of a barren area.