Harmful effects of Algae
Under certain conditions algae produce 'blooms', that is dense masses of material. This is especially true in relatively warm conditions when there is high nutrient availability, which sometimes is induced by man as and when sewage is added to water or inorganic fertilizers run off from agricultural land into rivers and lakes. As a result of this a sudden and explosive growth of these primary producers (algae) occurs. They are produced in such a huge quantity that they die before being eaten. The process of decomposition is carried out by aerobic bacteria which in turn multiply rapidly and deplete the water of oxygen. The lack of oxygen leads to the death of fish and other animals and plants in the lakes. The increase of nutrients which starts off the entire process is called eutrophication and if rapid it constitutes a major problem of pollution. The toxins produced by algal bloom can also lead to mortality. This can be a serious problem in lakes and oceans. Sometimes the toxins may be stored by shellfish feeding on the algae and be passed on to man causing the disease called paralytic shellfish poisoning. Algae also cause problems in water storage reservoirs where they may taint the water and block the beds of sand used as filters.