The second largest tributary of Lake Superior is the St. Louis River. The St. Louis is 179 miles long, and is almost entirely contained within St. Louis County, Minnesota. The river widens into a large bay and freshwater estuary near Lake Superior. The bay is separated from the lake by the largest sand bar in the world, which extends 12 miles between the twin ports cities of Duluth and Superior.
The sandbar had one natural opening to allow the outflow of the St. Louis River. First charted in 1861, the opening was as wide as 1500 feet, and 4 to 16 feet deep. Since then, the Superior Entry has been modified a number of times to meet the needs of ever bigger ships. The entry was dredged in 1871. Wood cribbing and a beacon were installed in the early 1880s. By 1885, a large installation was established on the north side of the entry by the Coast Guard. A steam powered fog signal was established in 1893. A second light was added in 1898. Concrete piers were added in 1905, and concrete breakwaters were completed in 1910. By 1912, a new lighthouse was built on the south breakwater. It featured an air powered fog signal and light with a fourth-order Fresnel lens. The air powered fog signal was retired in 1937 and replaced with a diaphone, which is a two-tone fog signal that works much like a pipe organ. The light station was automated in 1970.
Water levels in Lake Superior are impacted by a phenomena known as a seiche. That is, water sloshes back and forth across the lake, alternately piling up on either the east or west side of the lake. These seiches have a period of 7.9 hours. Water will flow east for 7.9 hours, then reverse and flow west for 7.9 hours. The water level in the harbor and bay rises and falls based on these seiches. The harbor has its own seiche on top of the Lake Superior seiche. The result is that water flow reverses direction at the Superior Entry every 2 hours and 6 minutes, alternately flowing out to the lake and back into the bay.
The final photo below shows the giant BNSF ore docks in the Superior harbor. The Northern Pacific dock #1 is on the very far right side of the photo behind the trees. You can see the light poles sticking up in the distance. The top photo has a much better view of the NP dock #1. The large docks in the center of the photo are the Great Northern dock #1 (right) and GN dock #2 (left). GN dock #3 no longer exists, and GN dock #4, as well as Burlington Northern dock #5, are out of the photo to the left. These three railroads all merged, and are now part of the BNSF. The NP and GN docks are no longer connected to the rail lines due to their low and narrow bridges over US-53 having been removed. The BN dock is still functional and did load some taconite in 2007, but its future is cloudy given the recent mine shutdowns. BN stores the taconite in a huge pile over a mile long west of the city of Superior. A conveyor belt brings the taconite to the to the ore loading facility. The ill-fated Edmund Fitzgerald filled up at the GN dock #1 in November, 1975, before it set out on its final voyage.
