Free-living photosynthetic bacteria and endosymbiotic plastids more commonly known as blue green algae, and are not plants. They are often visible as mats on the surface of water. Cyanobacteria are not plants or algae, although they are often referred to as blue-green algae (BGA) due to their blue-ish pigment phycocyanin. They are single celled photosynthetic bacteria which can live freely in the water column or as mats attached to sediment, rocks and plants. If nutrients are plentiful, they can form blooms (harmful algal blooms, HABs) and these can become visible at the surface of the water, especially when they are accumulated by winds and washed into a small bay or along a bankside. They are, however, an important component of freshwater ecosystems.