The concentration of the dissolved oxygen decides the quality of water in rivers, streams and lakes. When the concentration is more, the water quality is considered higher and better.
When pollutants like industrial or domestic sewage seep into the river or lake, micro-organisms begin to decompose the organic materials. Micro-organisms use up the dissolved oxygen in their metabolism. Very fast the oxygen is used up. The aquatic species such as fish begin to die and float around. When the oxygen level is reduced to zero; and the water is stated to be septic. Without oxygen the water produces bad odor. This foul smell is caused by the decomposed organic compounds. The putrid or septic conditions point it out to us that the dissolved oxygen is totally depleted.
Though the quantity of the sewage may be small by weight, the damage it can cause is huge. The impurities like organic materials are substantial. Food and vegetable waste form organic materials. The rotten plant nutrients, caused by chemical products such as soaps, detergents etc. Industrial sewage or domestic sewage generates disease-causing microbes. These microbes are the enemies of the man kind. And animals and plants suffer too.
How do we handle this issue? How do we dispose of the waste water? It is the responsibility of every citizen!
Why do we dump our garbage into the streams, lakes and rivers? How much of industrial waste, and domestic garbage is dumped into the Seas? There is no resting place for cans, bottles, polythene bags and wrappers, useless plastic products and footwear and many many unwanted household items. Vegetable oil and animal fat were the major ingredients used in the manufacturing process of soaps and other washing products. But today the petro-chemical industry produces synthetic detergents and washing products. And these petro-chemical products contain phosphates which soften the water among other damages. Does it ring a danger bell?
These chemicals in the washing products and detergents destroy the health of all living beings in water, such as fish etc.