Chroococcopsis fluviatilis is a species of cyanobacteria in the family Chroococcidiopsidaceae, documented from freshwater environments. Chroococcopsis is a genus of coccoid cyanobacteria characterized by cells that divide by multiple fission to produce smaller daughter cells called baeocytes, a reproductive mode that distinguishes this genus from related forms that divide only by binary fission. Cyanobacteria are prokaryotic photosynthetic microorganisms, among the most ancient forms of life on Earth, and are credited with producing the oxygen that transformed Earth's early atmosphere through the Great Oxidation Event approximately 2.4 billion years ago. Freshwater cyanobacteria play important roles in aquatic ecosystems as primary producers and, in some species, as nitrogen fixers that convert atmospheric nitrogen into forms usable by other organisms. Chroococcopsis fluviatilis inhabits flowing freshwater habitats as indicated by its specific epithet. Species in this group are typically identified by microscopic examination of cell morphology, arrangement, and division patterns, and many exhibit considerable morphological plasticity under varying environmental conditions. The species has not been assessed by the IUCN, consistent with the general treatment of prokaryotic microorganisms.