Cylindrospermum cells are cylindrical or barrel-shaped, measuring between 3-7 μm in width, slightly longer than they are wide. When observed under magnification, these cells appear blue-green or gray-green with a granular texture. They are arranged end-to-end to form long, unbranched filaments that are straight or gently curved. These filaments are surrounded by a clear, often transparent mucilage, which can cause them to form slimy mats on submerged vegetation or other surfaces. In addition to regular vegetative cells, one or both ends of the filament may contain pale blue heterocytes, specialized for converting dissolved nitrogen gas into ammonium essential for cell growth. The filaments may also feature one (sometimes two) large, blue-green or brown akinetes adjacent to the heterocytes. Akinetes serve as resting cells resistant to cold and other adverse environmental conditions, typically forming towards the end of the growth cycle and capable of overwintering in lake sediments.