1. INTRODUCTION The importance of river can be traced way back into history. The nomadic Stone Age man always wandered around rivers. The world’s greatest civilizations have flourished on the banks of rivers. The Nile River was a key for the development of Ancient Egypt, the Indus River for the development of Mohenjo-Daro civilization, the Tigris and Euphrates Rivers for the development of Mesopotamian cultures, the Tiber River for Ancient Rome, etc. Ever since man learnt the benefits of rivers, he has used the river for various purposes like drinking, domestic use, irrigation, navigation, fishing, etc. As man advanced he invented new techniques to exploit river waters. With the advent of industrialization, the river water was now being used as a way to dispose of industrial waste, sewage and other domestic waste. Today, success of human civilization in developing or under developing countries mostly depends upon its industrial productivity that leads to economic progress of the country. Urbanization, globalization and industrialization all have an indirect or not specifically intended effect on ecosystem (Tanner et al., 2001). The disposal of human waste is another great challenge in both developed and developing countries (Zimmel et al. 2004).Waterways have been considered as convenient, cheapest and effective path for disposal of human waste. Aquatic ecosystems have been threatened worldwide by pollution and non unsustainable land use. Effect of poor quality of water on human health was noted first time in1854 by John Snow when he traced the outburst of cholera epidemic in London Thames River which was polluted to a great extent by sewage. Industrialization, indiscriminate disposal of domestic waste, municipal waste, hospital waste, and run out of pesticides and fertilizers have disturbed the natural flow of water bodies. Nutrients are naturally present in water as they are required for healthy aquatic system and their balance isby natural water riparian system. But excess of nutrients introduced due the disposal of organic matter, untreated sewage etc. threaten the aquatic system. It has been observed that the level and concentrations of nitrogen and phosphorus has been nearly doubled due to domestic waste disposal and sewage water contamination in the water bodies (Harper 1992, McClain et al. 1998).As the nutrient content of water increases, there is a great increase in the phytoplankton in water. This in turn leads to lower dissolved oxygen content, causing fishes and other aquatic animals to die. There are two types of sources of pollutants - point sources and non-point sources. Point sources are sewage and industrial effluents. Though sewage treatment plants are used in some advance countries and C,Nand P are converted into their oxides. Again it has been discharged in to water bodies like river and which are soluble in water making it unfit for human consumption, if they cross the permissible limit. Non-point sources include the polluted runoff from agricultural fields, or wind-borne debris blowing out. Non-point sources are difficult to identify, extremely complex and their remediation are costly (Harnova, 2003).Natural process of water purification includes physical, chemical and biological processes. The physical process includes dilution, volatilization, sedimentation etc. The chemical process includes oxidation, reduction, dissolution, nitration etc. The biological processes include uptake or absorption and adsorption by plants, microorganisms, and microbial oxidation reduction etc.Excess uptake by plants; microorganism leads to a bloom of algae (blue green algae) causing eutrophication results in the formation of toxic metabolites. Nutrients retained by sedimentation come back to surface water and increase their concentration. Industrial effluents, discharge water from nuclear plant, dumping of hazardous waste, anthropogenic activity results in deposition of heavy metals, toxic metals into rivers. If their concentrations exceed permissible limit they cause ill effect. Consumption of such water directly by humans can cause serious problems. The fish living in such water eat plants that have small amounts of toxic substances in it. Smaller fishes are eaten by larger fishes, which will now have more concentration of toxic substances. This process continues throughout the food chain causing, the concentration of toxic substances increasing at each level. This is called bio- magnification. The Minamata disease at the Minamata Bay, Japan in the 1950’swas caused due to the consumption of fish containing Mercury. This Mercury had got into the bay water in the form of effluents from an acetaldehyde factory which used Hg as a catalyst. The symptoms of this disease were sensory impairment, hearing loss ataxia, speech disturbances. Though use of catalysts (like Hg) discontinued, long time after that the effects are still seen due to the accumulation of the metal in the food chain (bioaccumulation).Similarly, metals like Pb,As, Fe,Mn andCd beyond permissible limits cause severe ill effects (Mc Cohan et al. 1989). Thus it is necessary to monitor and have a check on them. By considering the possible hazards to the water environments due to different sources like sewage disposal, waste disposal, industrializations we have selected this topic for the study. Mithi River flows through the heart of the Mumbai city. It originates at Powai and meets the 2 Arabian sea near Mahim creek flowing through residential and industrial complexes of Powai,SakiNaka,Kurla, Kalina,Bandra-Kurla Complex, Dharavi,Mahim about 16-17 Km. The Mahim bay area where Mithi river meets the Arabian sea is nominated bird sanctuary called Saleem Ali Bird Sanctuary, where migratory birds come for resting, this part is full of mangroves which are the lungs for densely populated city Mumbai. At the beginning the river bed is narrow as it reaches Bandra-Kurla Complex it becomes wider. The river carries the storm water discharge (about 14 or more storm water outlets) as well as the sewage industrial effluents to Arabian Sea. As the Mithi River flowing through densely populated area, number of industrial units (authorized/unauthorized), slums of Dharavi, anthropogenic activity at bank, cattle sheds, dumping of hazardous waste has put question mark for quality of water in the river, the extent of pollution. Water is a very essential requirement of living things (Elixir of life).The availability of good quality water is indispensable need for healthy living. Declining the quality of water in most of the rivers in Indiae.g. River Ganga (Bhowmic et al., 1985), etc. and has threatened their sustainability and become cause of concern. The maintenance of healthy aquatic system (as per norm specified by WHO) have become a serious issue in India (WHO, Guidelines for drinking water quality recommendations, 2008). Healthy ecosystem is based on physicochemical properties and biological diversities. Monitoring the water bodies at regular intervals with respect to physicochemical and biological parameters will not only prevent outburst of water bound diseases but it will also have check on water quality preventing further deterioration of aquatic ecosystem. After disastrous floods In Mumbai in 26 July 2005, a project is taken up for cleaning of river, shifting the scrap dwellers, barrel cleaners, constructing the boundary walls etc.Due to the continuous deposition of organic matters, plastic materials, polythene bags, tobacco pouches etc. the flowing rate and caring capacity of the Mithi River and it was the main reason of the flood (MPCB, 2004). But even today a lot of anthropogenic activates are still going on. Waste water from industries such as dye industries, Garage waste, Sewage water without treatment has been discharged in the Mithi River. It is a great concern of pollution. Finally this polluted water transported or dumped in the in the Arabian Sea. Hence My topic ‘A Study of Water Quality of the River ‘Mithi’ in Mumbai Metropolis’ is a sincere effort to assess the quality of Mithi river 3 water and study the possible impacts of pollution which is a threat to the environment. The study will be useful for the management plans to control the river water pollution. 4 .