Dolichospermum lemmermannii, a filamentous cyanobacterium found in freshwater habitats, features long, unbranched filaments with cylindrical cells enveloped in a gelatinous sheath. Specialized heterocysts for nitrogen fixation are interspersed along the filament. Cells are typically 5-10 micrometers wide, and the organism is pigmented with chlorophyll a and phycobiliproteins, giving it a blue-green color. Reproduction occurs through filament fragmentation, aiding its spread in nutrient-rich waters. It plays a crucial ecological role in nutrient cycling but can form harmful algal blooms, impacting water quality in certain conditions.