The work deals with assessment of the water quality in the middle part of the small Carpathian stream Vydrica. Using benthic macroinvertebrates data, we calculated BMWP and ASPT indexes to compare the results of hydrobiological research from the years 1960, 1984 and 2006. We have found out, that the ecological water quality of the Vydrica stream has improved and has showed very good ecological quality. Because of Diptera are the dominant part of the benthic macroinvertebrates of the Vydrica stream, we have identified them into the genus and species level as possible. There were found some psammophilous taxa: Ptychoptera albimana , Scleroprocta sp., Eloeophila submarmorata , E. maculata / submaculata , Pilaria spp., and litophilous taxa: Liponeura vimmeri / decipiens preferring fast, well oxygenated water .