The groundwater in the alluvium aquifer of the Eskisehir Plain (EP) is polluted by wastewaters transported through Porsuk River, agricultural-industrial activities, river-groundwater interactions and unsanitary landfill. Porsuk River flows throughout the alluvium aquifer in the EP. In this study, the effects of anthropogenic activities on groundwater quality in the EP were investigated. Since the sewage system has been operated from 1998, the ammonia content of the groundwater has decreased, but the groundwater and Porsuk River water have high contents of nitrite, ammonium, phenol, phosphorus, AOX, sulphide, and heavy metals. Thus, groundwater in the EP is in a poor quality both for drinking and domestic purposes.