Chroococcus macrococcus is a cyanobacterium in the family Chroococcaceae, belonging to a group of unicellular to loosely colonial coccoid cyanobacteria distributed in freshwater and moist terrestrial environments. The specific epithet macrococcus refers to the large size of the cells, distinguishing this species from smaller-celled members of the genus. Chroococcus cells are characterized by their spherical shape, division by binary fission into pairs or tetrad arrangements, and enclosure within distinct gelatinous sheaths. The outer sheath layers are often visibly stratified in older colonies. Cyanobacteria of the Chroococcaceae occupy a broad range of aquatic and semi-aquatic habitats worldwide, from standing and flowing freshwaters to damp soil, rocks, tree bark, and the surfaces of other organisms. They are among the most ecologically resilient of photosynthetic microorganisms, tolerating desiccation, temperature extremes, and nutrient-poor conditions. Chroococcus macrococcus has been recorded from European freshwater localities. Its ecological significance lies primarily in contributing to primary production in aquatic communities. Like most microorganisms, it has not been formally assessed under IUCN criteria.