In this study, strong evidence of anthropic pollution was identified in the waters of the Boi Piguá River near the municipal landfill of Cascavel-PR. The elemental composition of the river water from five collection sites, the groundwater from four sites and the municipal landfill leachate were monitored over 1 year, using the total reflection X-ray fluorescence (TXRF) technique. Ten elements (Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, and Ba) were identified in the water samples. The elemental concentration data set was reduced to specific variabilities and characteristic clusters by applying cluster and principal component analysis (PCA). The greatest variability in concentration was observed in the Mn and Ba data, which formed the first, main component. A further three principal components were needed to explain the variability in the Ni, Cu, and Fe concentrations. According to the cluster analysis, samples from all the river and water table collection sites shared similarities with the landfill leachate composition. Thus, it is possible to affirm that the quality of the Boi Piguá River water has undergone major changes and an immediate intervention of environmental agencies is required.