a natural process of cleaning up the water through the action of microorganisms and other natural processes

a poison that damages the central nervous system

a condition in which the toxin is transferred  from one species to another, and accumulates in the bigger species as it eats more food

it means excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.

excessive growth and spread of algae and other water weeds in many bodies of water

a kind of algal bloom made up of phytoplanktons which are single-celled protists or plant-like organisms   

a condition characterized by a numbness of the lips, paralysis of extremities or death depending on how much toxins of a certain species of dinoflagellates  has been absorbed by the victim

considered the most carcinogenic compounds

it refers a body of water which could no longer support important aquatic species due to the depletion of oxygen and the deterioration of its natural conditions. 

this happens when hot wastewater usually from industrial or power plants  is released in rivers or lakes