Anabaena

A genus of filamentous cyanobacteria — the blue-green algae of ponds and reservoirs. Species such as Anabaena flos-aquae and A. circinalis can multiply into dense surface blooms in nutrient-rich fresh water, and some strains produce anatoxins, fast-acting neurotoxins dangerous to livestock, pets, wildlife and people. Blooms threaten drinking-water supplies and recreational waters, and can taint farmed fish with off-flavours. Water utilities watch cell counts through the warm months and treat affected water with activated carbon or oxidation to remove cells and toxins. Controlling nutrient runoff is the long-term defence against recurrent blooms.