The aim of this study was to evaluate the toxic effect in the bottom sediments of the Poraj Reservoir, along with defining their spatial distribution and the relationship between these elements and total heavy metal content (Zn, Cd, Pb, Ni, Cu). Samples of bottom sediments were collected on the basis of regular measurement grid of 46 points located in the area of the water reservoir Poraj. The collected samples were analyzed in terms of content of studied elements. Toxic effect was determined by Microtox®, which uses Vibro fishecri bacteria. Water extracts from bottom sediments caused less than 50% reduction in luminescence of bacteria. Total heavy metal content was determined on plasma spectrometer ICP-OES IRIS termo – mean values of total heavy metals content: Zn 461 mg·kg–1, Cd 1,4 mg·kg–1, Pb 50 mg·kg–1, Ni 12 mg·kg–1, Cu 17 mg·kg–1. By using of GIS system, spatial distribution of obtained results were interpolated (Inverse Distance Weighted method was used). Spatial analysis were made. There was no significant correlation between heavy metals and toxic effect.