In order to investigate the impact caused by the activities developed in the sulfur mine located in the close vicinity of the Neagra Şarului River, several biological material, sediment and water samples were collected. The water and sediment samples located closed to the mine proved to be highly acidic. The heavy metals identified in the river water samples were: Fe, Zn and Ni. Considering the heavy metals content, the water samples located closed to sulfur mine belong to the 5 th water quality class while the other samples can be classified as 1 st or 2 nd water quality class. The heavy metals identified in the sediments samples were: Cd, Cr, Pb, Ni, Zn and Fe. In 50% of sediment samples, Cu and Cd exceeded the maximum contaminant level set by the Romania Legislation. The water quality was also assessed using three biotic indices based on benthic invertebrate communities: the Extended Biotic Index, the Biological Monitoring Working Party adapted for Poland and the Average Score per Taxon. The level of saprobity and trophicity was calculated using bioindicator diatoms. The structure of the benthic invertebrate communities, together with their indicative values for water quality showed high polluted waters in the Neagra Şarului River and the Bistrița River. Bioindicator diatoms were absent on the Neagra Şarului River and the Bistrița River because of physico-chemical conditions.