Although draining such an immense area on which so many millions of human beings as well as domesticated animals live, the Mississippi River water just above New Orleans has been found to be remarkably free of pollution. This is due to the fact that the volume of the water is very great in proportion to the number of inhabitants on the water shed. The purity of the Mississippi water is largely due to dilution as well as to the chemical and mechanical processes of purification which are constantly going on within the flow of the stream. In spite of the vast amount of sewage which is poured into the river, only the merest traces of it can be detected at New Orleans.