Immersion of painted idols and dumping of organic wastes in the lakes, as a part of religious activities, are immensely adding to water quality deterioration. Incorporation of alkaline, alkali-earth metals and heavy metals through the idol-making paints are likely to promote the hardness and heavy metal concentration of water in these surface water bodies, and therefore, deteriorate the water quality. In this purview, periodic analysis of Nagavara and Ulsoor lake water was carried out to investigate the effect of idol immersion activities on the lake water quality. Water samples were collected before and after immersion activities randomly from different points of these lakes. In Nagavara lake, the maximum concentrations of calcium and magnesium were recorded to be 6.6 and 3.02 ppm, respectively after one month of immersion. The maximum concentrations of Na and K were 19.3and 42.8 ppm, respectively after seven days of immersion. In Ulsoor lake water, the EC had increased from 0.36 dSm-1 before immersion to1.22 dSm^-1 after 14 days of immersion. The nitrate content of water before immersion was 1.51 ppm which increased to4.7 ppm, after 14 days of immersion in Ulsoor lake water. Higher BOD and COD values were recorded in lake water seven days after immersion activities. The concentrations of different inorganic ions including heavy metals (Cr, Cd and Pb) were found to increase in the post-immersion period. The water of these lakes is used for irrigation as well as other purposes. Thus, proper measures have to be adopted to restore and maintain water quality in these lakes.