Background: Benthic macroinvertebrates are commonly used as indicators of the biological condition of waterbodies. Both the benthic macroinvertebrates and the physicochemical properties of the water provide important information about the pollution of a water environment. Goals: To investigate the relationships between assemblage composition of Oligochaeta (Annelida), Chironomidae (Diptera), and other macroinvertebrates with physical and chemical water variables in the Meric River, Turkey. Methods: This study was carried out by taking water and benthic samples at 8 stations at monthly intervals in order to determine what macrobenthic fauna exist in the Meric River and what environmental properties affect their distribution. Results: A total of 39 taxa were found and we determined that there is an average of 851 individuals per m(2). Also, this study established the first records for Brachium sowerbyii (Oligochaeta) and Pottashia alternis (Chironomidae) in the Turkish Thrace region. According to Shannon-Wiener index, while it was determined that Meric River has the highest diversity values with H' = 0.845 at the station 4, the river has the poorest diversity with H'= 0.477 at the station 2. Also, we examined similarities of distribution of Oligochaeta taxa by station and month using the Bray-Curtis index. Accordingly, while stations 6 and 8 were determined to be the most similar to each other, stations 2 and 5 were the least similar. The relationships between Oligochaeta taxa and physical and chemical parameters of water were evaluated using the Spearman Correlation index. As a result, we found that water temperature, pH, electrical conductivity, hydrogen sulfide, calcium, magnesium, phosphate, chlorine, salinity, dissolved oxygen and biological oxygen have positive correlations with some species of Oligochaeta, while nitrate and nitrite have negative correlations with some species of Oligochaeta. Conclusions: We made a number of suggestions for sustainable usage of this river.