The most commonly used chemical fertilizers, ammonium sulfate, urea, super phosphate and the like, are used in large amounts, only fractions of which are absorbed by the plants in the field. The rest leaches into streams and rivers, eventually flowing into the Inland Sea. These nitrogen compounds become food for algae and plankton which multiply in great numbers, causing the red tide to appear. Of course, industrial discharge of mercury and other contaminating wastes also contribute to the pollution, but for the most part water pollution in Japan comes from agricultural chemicals.
