The study attempts water quality monitoring of Mansar lake to detect the various water quality parameters. The lake water conditions were monitored by collecting water samples from different depths to determine the spatial and temporal variations.

pH value of the lake was found to vary from 7.8 at the bottom of the lake to 8.2 at the surface of the lake. Temperature decreases with depth in the month of July while in January it remains the same at all depths. On the basis of temperature in July, Mansar lake can be classified into epilimnion zone (surface to 3m depth), thermocline (3 to 9m depth) and hypolimnion (below 9m depth). Temperature variation indicates that mixing of the lake water takes place in winter and remains stratified in rainy and summer season.

The electrical conductivity, hardness and alkalinity vary with depth. Calcium, Sodium and Magnesium are dominant cations, and bicarbonate is the dominant anion. The presence of cations in the lake water is observed as Calcium > Sodium > Magnesium > Potassium and anions as Bicarbonate > Chloride > Sulphate > Nitrate > Phosphate.

The concentration of phosphorous is more than 0.03 mg/l, which is characteristic of eutrophic lakes. Anthropogenic activities have accelerated the eutrophication process in the lake. Bottom zone in the lake is deficient in oxygen and shows anoxic conditions. Physico-chemical parameters of lake water were found within the limits of Class A drinking water except for Dissolved Oxygen (DO). DO value is less than 6 mg/l below 3m depth in July and below 15m depth in January. This means that water between 3 to 15m depth is more suitable for drinking purposes. The study reveals that the water from the lake is suitable for irrigation purposes.

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