Planktothrix agardhii is a cyanobacterial species that typically forms filamentous colonies consisting of cylindrical cells arranged end-to-end in unbranched filaments. Each cell is relatively small, generally about 3 to 5 micrometers wide, and varies in length based on its environment. These cells are enveloped in a mucilaginous sheath that helps maintain filament cohesion and potentially aids in their buoyancy in water. Found commonly in freshwater habitats such as lakes and ponds, Planktothrix agardhii plays crucial roles in aquatic ecosystems through processes like photosynthesis and nitrogen fixation. Under certain conditions, this species can produce toxins that affect water quality and pose risks to other organisms within the ecosystem.