Dolichospermum crassum is a filamentous cyanobacterium found in freshwater environments. It forms unbranched trichomes of cylindrical cells, which can be straight or slightly curved. The trichomes include specialized heterocysts for nitrogen fixation and produce akinetes for survival. Cells are typically 2 to 6 micrometers wide and 5 to 20 micrometers long, containing pigments for photosynthesis and having a blue-green coloration. This species contributes significantly to nutrient cycling and supports aquatic ecosystems through primary production and nitrogen fixation.