Slow transformation of a vibrant water area to a marsh or bog. Death by shallowing and algae is the end-point if not reversed.. Root cause is the dumping or concentrating of pollutant nitrogen and phosphorus, be it elemental or in a compound. Algae population literally explodes in these conditions. As algae decays it consumes the water oxygen. This kills all non-algae water life, both plants and animals. Human action is the event driving the pollution.