Water quality monitoring was carried out for various physicochemical, bacteriological characteristics and trace elements in the Renuka lake. Water quality of the lake was assessed for drinking purposes based on Bureau of Indian Standards, which showed degradation due to various anthropogenic activities. The results showed BOD:COD ratio in the order of 0.44. The Dissolved Oxygen (DO) varies from 2 mg/L (surface) to 10.4 mg/L (bottom), showing bottom of the lake under anoxius condition. A few water quality parameters (viz., TDS, TH, Ca, Mg, DO, total coliform, faecal coliform, Fe, Pb, Mn, Cu, Cd) exceeded the prescribed desirable limits for drinking purposes. The eutrophication assessment showed the lake under hypereutrophic condition. The eutrophication level of the lake showed a decreasing trend, which is an indication of some improvement in the lake water quality, because of adopting measures for conservation by the state government. Based upon the CPCB classification of water, the lake water was classified for outdoor bathing (organized). The water balance of the lake showed that it receives a major component of input water through runoff (RO:61.1%) from the catchment. Various anthropogenic activities in the lake/catchment (viz., grazing, felling of trees, fish feeding, dumping of wastes i/c residue of flesh feeding to zoo animals, fertilizer application, etc.), should be restricted.

Renuka lake, situated in the valley of lesser Himalayas of the Himachal Pradesh, is surrounded by mountains consisting of highly crumpled, shattered, crushed, folded and dislocated rocks besides carbonaceous shales-slates often pyrite-ferrous, limestone, quartzites, boulder beds, etc. (Das and Kaur, 2001). This lake has a great religious significance in the Himachal Pradesh. It is a part of an abandoned tract of the river Giri. Apart from regular tourists, thousands of devotees reach the lake during its state level annual fair near Renuka lake/catchment and people feed fish with grain flour pills. It is also one of the reasons for water pollution in the lake.

Renuka lake is shrinking due to siltation, pollution and growth of weeds. Various activities like deforestation, grazing, culture practices and improper agricultural land use without environmental safeguard is causing widespread deterioration of its soil-water ecosystem. These activities not only trigger silting of the lake but also contribute significant quantity of nutrients and organic matter which initiate the process of eutrophication affecting overall use of the lake water. Since, the lake is surrounded by hills, the runoff emerging from surrounding hillocks drain into this lake causing heavy siltation and reducing its water storage capacity. The extent of human activities which influence the environment has also increased during past few decades and has affected the natural hydrochemical cycle of this water body (Anonymous, 1996).

Environmental Sciences Journal, Physicochemical Characteristics, Bacteriological Characteristics, Dissolved Oxygen, DO, Natural Hydrochemical Cycle, Hydrometeorological Data, Global Water Intelligence, GWI, National Institutes of Health, NIH, Biochemical Oxygen Demand, BOD, Chemical Oxygen Demand, COD.