<ul><li>Water pollution is any chemical, biological, or physical change in water quality that has a harmful effect on living organism or make water unsuitable for desired uses.</li></li></ul><li>The Causes Of Water Pollution <br />
Table of Sources, pollutants, and effects of water pollution<br />
Eutrophication is a natural process whereby an aquatic ecosystem becomes enriched with nutrients causing an excessive growth of aquatic plants.<br />Nutrients can come from many sources such as:<br /><ul><li>Fertilisers (especially Nitrates and Phophates) from agricultural fields.
Run-off of animal waste.</li></li></ul><li>The increased nutrients promote rapid growth of algae when they are deposited in rivers, lakes and streams.<br />The excessive growth of algae is often called an algal bloom.<br />
Algal blooms endanger the ecosystem in 2main ways.<br />1,<br />The densely populated algae cover the water surface and block sunlight. Unable to carry out photosynthesis, the aquatic plants die.<br />When these plants die, aquatic animals lose their food sources and habitats. As a result, the food chain and ecosystem change.<br />Algae also reduce the level of dissolved oxygen in the water.<br />2,<br />When the algae and other aquatic organisms die, decomposing organisms especially saprophytic bacteria use up oxygen to decompose the dead organic materials.<br />This reduce the oxygen content in the water.<br />
A depletion in oxygen results in an increase in biochemical oxygen demand (BOD).<br />Eutrophication increase the BOD value in the water.<br />BOD refers to the amount of oxygen utilised by microogranisms to oxidise all organic matter in one litre of water.<br />The higher the BOD value, the more polluted the water as the dissolved oxygen level decrease. <br />