The pollution of the water supplies threatens injury to the people of the United States in two principal ways. In the first place the pollution of the streams is destroying the fish supply, thus removing a very important source of food. Further than this, the pollution of the streams entering the sea, especially near large cities, is so great that the oyster and clam supplies are polluted, thus threatening the health and life of the citizens of the country.

The second threat to the prosperity of the country is in the pollution of the water supply for human consumption. The United States Government, through the Department of Agriculture, and the public health service and the state governments in many states is endeavoring to minimize the pollution of the running streams. As the population grows denser and manufacturing industries are more widely scattered, the threat of pollution becomes greater. In looking to the future control of the running streams it is evident that the states and the government must continue to cooperate, by reason of the fact that the state can control the stream only within its borders, while the United States can control the streams only as they flow from one state to the other. Thus, for complete control both sets of authorities must act.

Flow Through the Chicago Canal.1 - The authorized flow through the canal was fixed by the War Department at 4,167 cubic feet per second, but at the present time and for a number of years past, the flow has averaged approximately 8,000 cubic feet per second. This diversion has of course, lowered the lake level to a certain extent, probably not over a few inches, but owing to the natural fluctuations of the level of Lake Michigan the amount of such lowering cannot be determined without elaborate calculation. A very complete discussion by the U. S. Lake Survey of the probable effect on lake levels of the diversion of their waters is given on page 5401, Annual Report, Chief of Engineers, 1900 and pages 4120-4131, Annual Report 1904.

The level of Lake Michigan is constantly fluctuating. Local and temporary oscillations of irregular amount and duration occur frequently. These oscillations which are due to the influence of wind and changes in barometric pressure, sometimes amount to as much as five feet, but average considerably less than one foot per day. In addition to these temporary oscillations, there is a consistent seasonal change in level during each year, the highest stage occurring during the summer months. Since 1860, the greatest annual change in elevation between the highest and lowest monthly mean of any year is given by the U.S. Lake Survey as 2.23 feet and the least annual fluctuation as 0.57 foot. The mean annual level varies from year to year but without any regularity. Since 1860 the maximum variation between the highest and lowest monthly mean during the whole period was 4.59 feet.

1Letter from War Department District Engineer, Chicago, April 26, 1918.