The development of irrigated agriculture has multi-directional benefits for the economic development of a country. However, it has negative consequences including environmental effects, land degradation, waterlogging, salinization, and social instability when the irrigation water is not properly managed. This research has been conducted at Koga Irrigation Scheme to assess the effect of irrigated agriculture on spatial and temporal fluctuations of the groundwater table and water quality. This study has attempted to highlight the status of spatial and temporal fluctuations of the groundwater table depth at Koga irrigation scheme, Northwest Ethiopia. Purposive representative samples of six shallow wells inside the irrigation scheme and four shallow wells outside the irrigation scheme were selected for evaluation of the impact of irrigation on groundwater table fluctuation and groundwater quality. Arc GIS tool has been applied for interpolation of the spatial variation of the groundwater level. The result of the study clearly showed that irrigation has affected the groundwater level and groundwater quality. For instance, under the irrigated field, a rise in the groundwater table that ranges from 0.77 m to 0.52 m observed compared with non-irrigated field. The groundwater table was found to have high fluctuation in space and time owing to spatial and temporal variation of irrigation amount, soil type, topography, and other factors. The groundwater quality also showed that the concentration of nitrate and sulfate was higher in the irrigated land than non-irrigated land. However, the concentration of the nutrients was below the world health organization drinking water quality parameters. This study indicated the need to pay more attention to the irrigation water management of the scheme to control the groundwater level rise. This study showed that irrigation has effect on groundwater level and there is high spatial and temporal variation of groundwater level in the area. Therefore, continuous follow-ups and assessment of the groundwater table and Physico-chemical properties of the study area is essential for the sustainability of the Koga irrigation scheme and human health of the people who live in the scheme.