The aim of this study was to examine TC (total coliforms) and coli titter from two sampling stations in the aquatory of Kardzhali Dam Lake and one station in River Arda, in August, 2011. The values of the TC index in the reservoir vary from 1900±674 cfu/100ml in station I, to 1293±194 cfu/100ml in station II, while the TC value of River Arda reaches 1698±134 cfu/100ml. In Reservoir Kardzhali, the smallest volume of water in which Escherichia coli cells were found, varies between 5 and 15 ml, while for the River Arda the value of coli titter is equal to 1. With highest percentage, regarding the presence of microbiological species in the reservoir waters, is the genus Klebsiella (70%), followed by Citrobacter (15%), Enterobacter (10%) and Serratia (5%), respectively represented by the species Klebsiella oxytoca, Citrobacter freundii, Enterobacter cloacae and Serattia marcescens. In the river Arda two genuses were found - Serratia (50%) and Salmonella (50%).