Changes in modern life style and use of heavy amounts of agrochemicals and fertilizers have caused a scenario due to which there are undesired changes in physico-chemical parameters of water, soil and air. Anthropogenic activities thus have enhanced the quantum of pollution of fresh water ponds and Mons. Water quality has tremendous impact on flora and fauna. Manika Mon is a perennial water reservoir of Muzaffarpur. Because water of this Mon is being used for different purposes, so its physico-chemical analysis was done in different seasons. Temperature of surface water was taken from February to March, May to July, August to September and November to January. Similar studies were also conducted for different parameters. The mean of the data for pH varied from 7.10 May to July, to 8.30 from February to March. In the same periods temperature varied from 13.6 0 C to 29.5 0 C. Turbidity varied between 48.0 cm to 116 cm, soluble substances from 1022 mg to 1150 mg/l, while dissolved oxygen varied between 5.62 mg/l to 10.16 mg/l , free carbon dioxide 12.58 mg/l to 16.72 mg/l, chloride 28.75 mg/l to 47.70 mg/l, calcium 6.18 mg/l to 12.19 mg/l and Ca-hardness 8.26 mg/l to 19.71 mg/l. Therefore, it is essential that the water body should be put under strict vigilance and constant monitoring so that the water should be maintained at its better quality.