The effect of 19 environmental variables on species richness of macrophytes was studied in 39 Slovak streams. The studied streams were poor in species; in total, 88 macrophyte taxa were found and the average number of macrophytes per sampling site was 4, ranging from 0 to15. The most frequently occurring macrophytes were filamentous algae (occurrence at 38.6% of sampling sites), followed by Rhynchostegium riparioides (28.4%) and Phalaris arundinacea (19.3%). The strongest environmental gradient in the sampling site detected by factor analysis (factor 1 explains more than 32% variability) is related to the portion of artificial banks, shading by woody vegetation along banks, flexuosity of stream course and the portion of natural land cover in the contact zone of the stream, and can be interpreted as a natural-anthropogenic gradient. The following variables had the highest correlations with species richness of macrophytes: shading by woody vegetation ( r=−0.507), portions of artificial bank ( r=0.488), flexuosity ( r=−0.457) and distance from stream source ( r=0.388). [ABSTRACT FROM AUTHOR]