Ambient air quality monitoring was carried out in the vicinity of dam and nearby residential sites in four river basins in Karnataka with reference to SPM, RSPM, SO2 and NOx, employing Envirotech APM-460 Respirable Dust Sampler with provision to keep impingers having absorbing reagent. Further, three different methods of Air quality index (AQI) calculation on based on SPM and RSPM values were used to evaluate the prevailed ambient air quality in the near and surroundings areas at the time of dam constructional activities. The concentrations of SPM, RSPM, SO2 and NOx near the dam sites were respectively 540, 170, 5.8 and 17.9 ug/m3 in Varahi river basin; 440, 158, 3.8 and 11.4 ug/m3 in SLIS river basin and, 255.55, 83.3, 2.0 and 1.7 ug/m3 in SRLIS river basin. The SPM, RSPM and SO2 concentrations was 340, 70 and 0.3 ug/m3 in the vicinity of dam site of Bellary nala river basin while NOx concentration was below the detectable limit. AQI calculations revealed that the dam sites in all four river basins were high to severely pollute compared to other monitored stations, owing to its construction activities.