Cyanobacteria species of Yamchia reservoir of drinking and irrigation waterof Ardabil Province (northwest Iran) was studied from October 2013 to November 2014. In this paper arewiew of identified species are presented. A total of 16 species belonging to 11 Genera, 9 Families and 4 Orders were identified, from which 10 species are planktic. Microcystisaeruginosa and Aphanizomenonflosaquaewere most abundant species in surface water during summer months, mainly due to regulating their buoyancy via gas vescicles.In general Oscillatoriais the most dominant Genus in the region with 4 species including Oscillatoriacurviceps, Oscillatorialimosa, Oscillatoriaprincepsand Oscillatoriatenuis.