Objective:The aim of the study was to determine the prevalence of Blastocystis subspecies in water samples collected from Ordu province.Methods:Seventy-five surface water samples and 25 drinking water samples were collected from Ordu and its boroughs. The samples were flocculated by aluminum sulphate and concentrated by sucrose gradient method. Small subunit ribosomal RNA (SSU rRNA) gene was amplified by polymerase chain reaction (PCR). Sequence analysis was performed on the positive PCR products and the base sequences were aligned using Bioedit. Phylogeny trees were drawn and Blastocystis subspecies were identified.Results:Four out of the 100 water samples were positive for Blastocystis spp. No positivity was found in the drinking water. Blastocystis ST-1 subspecies was detected in Bülbül River, Kacalı River and Bolaman Stream. Blastocystis ST-3 subspecies were found in Karabalçık River. The lowest genetic distance was found between ST-1 subspecies and the samples from Bülbül River, Kacalı River and Bolaman Stream. The nucleotide similarities between them were 98.8%, 76.6 and 98.8%, respectively. The lowest genetic distance was found between Karabalçık River and ST-3 subspecies and the nucleotide similarity between them was 99.1%.Conclusion:This is the first study on the presence of Blastocystis spp. in the surface water and drinking water samples in Ordu province of the Black Sea area in Turkey.