Explanation:

Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use”.
The general types of ecological consequences include: reduction in biodiversity, die-off of certain organisms, reduction in visibility and mobility functions due to biotic overgrowth (which effects can interfere with plant metabolism and with aquatic animal transport); reduction in dissolved oxygen and associated fitness reduction in animals dependent upon oxygen levels.
When algae die, they decompose and the nutrients contained in that organic matter are converted into inorganic form by microorganisms. This decomposition process consumes oxygen, which reduces the concentration of dissolved oxygen. The depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity.