● Human beings have been `color{violet}"abusing the water-bodies"` around the world by using them for `color{violet}"disposal of all"` `color{violet}"kinds of waste"`.

● We tend to believe that `color{violet}"water can wash away"` everything not taking cognizance of the fact that the `color{violet}"water bodies"``color{violet}" are our lifeline"` as well as that of all other living organisms.

● Due to such activities of human kind the`color{violet}" ponds, lakes, stream"`, `color{violet}"rivers, estuaries and oceans"` are becoming polluted in several parts of the world.

● Realising the importance of `color{violet}"maintaining the cleanliness"` of the water bodies, the Government of India has passed the `color{Brown}"Water (Prevention and"` `color{Brown}"Control of Pollution"``color{Brown}") Act, 1974"` to safeguard our water resources.

● As we work with water in our homes in the cities and towns, we `color{violet}"wash everything into drains"`.

● A mere `color{violet}"0.1 per cent impurities"` make domestic sewage `color{violet}"unfit for human use"`.

● `color{violet}"Solids"` are relatively `color{violet}"easy to remove"`, what is difficult to remove are dissolved salts such as `color{violet}"nitrates, phosphates"`, and other nutrients, and `color{violet}"toxic metal ions"` and `color{violet}"organic compounds"`.



● Domestic sewage primarily contains `color{violet}"biodegradable organic matter"`, which readily decomposes – thanks to `color{violet}"bacteria"` and other micro-organisms, which can multiply using these `color{violet}"organic substances as substrates"` and hence utilise some of the components of sewage.

● It is possible to estimate the `color{violet}"amount of organic matter"` in sewage water by measuring `color{Brown}"Biochemical Oxygen Demand (BOD)"`.

● Micro-organisms involved in `color{violet}"biodegradation of organic matter"` in the receiving water body consume a `color{violet}"lot of oxygen"`, and as a result there is a `color{violet}"sharp decline in"` `color{violet}"dissolved oxygen"` downstream from the point of sewage discharge.

● This causes `color{violet}"mortality of fish"` and other aquatic creatures.

● Presence of `color{violet}"large amounts of nutrients"` in waters also causes `color{violet}"excessive growth of planktonic"` (free-floating) `color{violet}"algae"`, called an `color{Brown}"algal bloom"` which imparts a `color{violet}"distinct colour"` to the water bodies.

● Algal blooms cause `color{violet}"deterioration"` of the `color{violet}"water quality"` and `color{violet}"fish mortality"`.

● Some `color{violet}"bloom-forming algae"` are extremely `color{violet}"toxic"` to human beings and animals.

● Very common are the `color{violet}"beautiful mauve-colored flowers"` found on very appealingly-shaped floating plants in water bodies.

● These plants which were `color{violet}"introduced into India"` for their lovely flowers have caused havoc by their `color{violet}"excessive growth"` by causing blocks in our waterways.

● They `color{violet}"grow faster"` than our ability to remove them.

● These are plants of `color{violet}"water hyacinth"` (𝘌𝘪𝘤𝘩𝘩𝘰𝘳𝘯𝘪𝘢 𝘤𝘳𝘢𝘴𝘴𝘪𝘱𝘦𝘴), the world’s most problematic `color{violet}"aquatic weed"`, also called `color{brown}"Terror of Bengal"`.

● They grow `color{violet}"abundantly in eutrophic"` water bodies, and lead to an `color{violet}"imbalance in the ecosystem"` dynamics of the water body.

● `color{violet}"Sewage"` from our homes as well from hospitals are likely to contain many `color{brown}"undesirable pathogenic microorganisms"`, and its disposal into a water without proper treatment may cause outbreak of serious diseases, such as, `color{violet}"dysentery, typhoid"`, `color{violet}"jaundice, cholera"`, etc.

● Unlike `color{violet}"domestic sewage"`, waste water from industries like `color{violet}"petroleum, paper manufacturing"`, `color{violet}"metal extraction and processing"`, `color{violet}"chemical manufacturing"`, etc., often contain toxic substances, notably, `color{brown}"heavy metals"` (defined as elements with `color{violet}"density > 5"` `g/(cm)^3` such as `color{violet}"mercury, cadmium"`, `color{violet}"copper, lead"`, etc.) and a variety of organic compounds.

● A few `color{violet}"toxic substances"`, often present in industrial waste waters, can undergo `color{violet}"biological magnification"`
(`color{brown}"Biomagnification"`) in the aquatic food chain.

● Biomagnification refers to `color{violet}"increase in concentration"` `color{violet}"of the toxicant"` at `color{violet}"successive trophic levels"`.

● This happens because a toxic substance accumulated by an organism `color{violet}"cannot be metabolised or excreted"`, and is thus `color{violet}"passed on"` to the next higher trophic level.

● This phenomenon is well-known for `color{violet}"mercury and DDT"`.

● In this manner, the `color{violet}"concentration of DDT"` is increased at `color{violet}"successive trophic levels"`; say if it starts at `color{violet}"0.003 ppb"` (ppb = parts per billion) in water, it can ultimately can reach `color{violet}"25 ppm"` (ppm = parts per million) in `color{violet}"fish-eating birds"`, through biomagnification.

● High concentrations of `color{violet}"DDT disturb calcium metabolism"` in birds, which causes `color{violet}"thinning of eggshell"` and their `color{violet}"premature breaking"`, eventually causing `color{violet}"decline in bird populations"`.