I quote the article here: "Great Britain and the United States are each to be given perpetual access to the Mississippi River".
What is the significance and legal ramifications of shared access of the Mississippi, does this mean that the U.S government must always provide access to British citizens regardless of visa limitations (I guess I'm asking, today, can a British subject go to America, and claim Art. 8 as a free-entry card to the U.S via the MS river)? And is there a commercial element to the article (when they mean access, do they mean commercial access to fishing?)
This article was drafted at a time when inadequate surveying led both parties to believe that the Mississippi River extended as far north as Lake of the Woods. As Article 2 states in part, the border was to travel:
... "thence through Lake Superior northward of the Isles Royal and Phelipeaux to the Long Lake; thence through the middle of said Long Lake and the water communication between it and the Lake of the Woods, to the said Lake of the Woods; thence through the said lake to the most northwesternmost point thereof, and from thence on a due west course to the river Mississippi; thence by a line to be drawn along the middle of the said river Mississippi until it shall intersect the northernmost part of the thirty-first degree of north latitude" ...
Because the border was thought to rely upon the Mississippi, the right to travel that river was a piece of forethought by the British, who believed it might be useful to reach far western Canada.
As subsequent surveying proved, the Mississippi never reaches the latitude of Lake of the Woods. This problem was resolved in the Anglo-American Convention of 1818, whose second article said the American-Canadian border should travel from the most northwestern point of Lake of the Woods, then along the 49th Parallel to the "Stony Mountains," the name then given to the Rocky Mountains.
This treaty itself created two problems. The first was that because the boundary extended only to the Rockies, it caused the Oregon boundary dispute that was settled only by extending the border all the way to the Pacific along the 49th Parallel.
The second problem, one that still exists today, is that the most northwestern point of Lake of the Woods is a good distance north of the 49th Parallel. As a result, the state of Minnesota has an interesting little enclave that is accessible only by driving through Canada or traveling across Lake of the Woods. On maps of the world, it's shown by a small "bump" in the northern border of Minnesota.
In other words, Article 8 was overridden by subsequent treaties.