What environmental problems does water pollution cause?

It causes loss of coral reefs and animals, also transferring to all over the world. Your trash could start at France and end up in Indonesia.

In the mainland, water pollution containing nitrogen and phosphorus encourage explosions in growth of algae, which eventually die off giving off carbon dioxide in the water and using up oxygen. This CO2 kills other plant and animal life, rendering the lake, river or pond lifeless. Eventually these bodies of water dissappear forever because of this growth.