Algae the plant like microorganisms are prolific invaders of the open exposed parts of cooling systems such as the tower and the pond areas. They will grow rapidly if conditions are right and only require light; CO2 and water to synthesize their growth. Algae are often visible as green felt-like mats in internal sections of cooling towers that are wet and accessible to sunlight. Algal growth is extremely unsightly and will reduce the efficiency of the cooling tower as a heat exchanger. Loosened deposits will block and foul pipe work and other heat exchange surfaces. The dead cells contribute to the formation of the complex organic material Humus which supports the growth of other microorganisms particularly the anaerobic types. Filamentous and capsulated colonial algae coat splash packing thus interfering with the formation of droplets which aid intimate contact of water and air. Algal growth prevents rainwater from wetting film packing and forming thin films which are Algae also secrete a mucilaginous sheath much like the slime layer in bacteria. The mucilage of the blue-green algae in particular is associated with a peculiar form of movement called gliding that is exhibited when the organism is in contact with a firm surface. These sticky secretions may contribute significantly to complications in cooling systems such as clogged screens and fouled heat exchangers. Many algae produce within their cells malodorous oils and poisonous cyclic alcohols these are released when the organisms die and may cause foul odours.