SAINT CLAIR RIVER, the outlet for Lake Huron, which in turn receives the waters from Lakes Superior and Michigan. Forming part of the boundary between the State of Michigan and the Province of Ontario, Canada, it flows in a southerly direction into Lake St. Clair with a fall of about 5.8 ft. in 4o miles. The river discharges through seven mouths, the one known as the South channel being used for deep-draught vessels, while several of the other channels are used for small craft. The South channel has been improved by the dredging of separate channels for up-bound and down-bound traffic, extending from deep water in the river into Lake St. Clair.
The project for the main improved channel through the river calls for a minimum depth of 20 ft. when the levels of Lakes Huron and St. Clair are at low water datum. The U.S. Congress in 1928 gave consideration to increasing the depth of this channel in connection with a programme for general deepening of all the main connecting channels of the Great Lakes, and some increase will probably be authorized in the near future. The
water level of this river fluctuates with the levels of the lakes above and below. During the past 20 years the difference between the highest and lowest monthly mean levels during the navigation season has been about 4 feet. Occasional fluctuations due to winds of high velocity may be 3.5 ft. in six hours.
Near the head of the river are located the cities of Port Huron, Mich., and Sarnia, Ontario, both of which handle some water borne commerce but the great bulk of the traffic moves through the river without intermediate stop. This traffic in 1927 totalled 89,000,00o tons, composed principally of iron ore, grain and limestone down-bound and coal up-bound.