ABSTRACT: The Sereď region has long been affected by environmental pollution; mainly from the nickel smelter industry, and this report therefore assesses the environmental impacts of the Sereď Nickel smelter on groundwater and sediment. The groundwater pollution was monitored in 25 wells in 2013 – 2015, and sediment quality was observed in the river Váh bay in 2015. Monitoring revealed that the most polluted groundwater wells are in close proximity to landfill waste mud from the nickel smelter where NH4+, Ni and high SO4, Zn and B concentrations were found with other components. However, the elevated NO3-, NH4+ and SO4 levels observed in wells south and southeast of the pollution sources in the groundwater flow direction were due to intensive farming as well as smelter operation. Excessive amounts of Ni and Cr were also revealed in river Váh bay sediment which is mostly slag in heating plant ash from the former iron works. While nickel can leach in the sediment, this leaching is not proven for accompanying chromium, and although the Decree of the Ministry of the Environment 310/2013 Coll. considers nickel leached with distilled water in the sediment samples is non-hazardous waste, our results confirm the necessity to continue monitoring individual environmental components; especially affected water and solids in sediment and soil.