This aim of this study was to test the applicability of diatom indices developed in Europe for monitoring coastal stream waters in northern Poland. Water, sediment, and diatom samples were taken from streams in the resort town of Sopot that discharge into the Gulf of Gdansk. The physical and chemical measurements taken during the sampling period indicated that the purity of the stream waters had improved, and recently they were classified as I class water purity. This is contrasted by the studied waters? diatom communities, which were dominated by eutraphentic taxa. High abundances of -mesosaprobic and -mesosaprobic taxa were recorded at most of the sites. Diatom indices developed for water quality surveillance were calculated with the Omnidia3 database software. Redundancy analyses (RDA), an ordination technique, was used to determine the indices that best correspond to water pollution in coastal streams. The results of the present study indicate that the pollution indices that follow can be applied successfully to monitor flowing freshwaters in the Gulf of Gdansk area in northern Poland: IDAP (Indice Diatomique Artois-Picardie); SPI (Specific Polluosensivity Index); EPI-D (Eutrophication/Pollution Index based on Diatoms), which integrates organic pollution, eutrophication, and mineralization.