through, among other outlets, South Pass, separating Cat Island from Isle à Pitre.

If the doctrine of the thalweg is applicable, the correct boundary line separating Louisiana from Mississippi in these waters is the deep water channel.

The term "thalweg" is commonly used by writers on international law in definition of water boundaries between States, meaning the middle or deepest or most navigable channel. And while often styled "fairway" or "midway" or "main channel," the word itself has been taken over into various languages. Thus in the treaty of Luneville, February 9, 1801, we find "le Thalweg de l'Adige," "le Thalweg du Rhin," and it is similarly used in English treaties and decisions, and the books of publicists in every tongue.

In Iowa v. Illinois, 147 U. S. 1, the rule of the thalweg was stated and applied. The controversy between the States of Iowa and Illinois on the Mississippi river, which flowed between them, was as to the line which separated "the jurisdiction of the two States for the purposes of taxation and other purposes of government." Iowa contended that the boundary line was the middle of the main body of the river, without regard to the "steamboat channel" or deepest part of the stream. Illinois claimed that its jurisdiction extended to the channel upon which commerce on the river by steamboats or other vessels was usually conducted. This court held that the true line in a navigable river between States is the middle of the main channel of the river.

Mr. Justice Field, delivering the opinion of the court, said: "When a navigable river constitutes the boundary between two independent States, the line defining the point at which the jurisdiction of the two separates is well established to be the middle of the main channel of the stream. The interest of each State in the navigation of the river admits of no other line. The preservation by each of its equal right in the navigation of the stream is the subject of paramount interest. It is, therefore, laid down in all the recognized treatises on inter

VOL. CCI-4

national law of modern times that the middle of the channel of the stream marks the true boundary between the adjoining States up to which each State will on its side exercise jurisdiction. In international law, therefore, and by the usage of European nations, the term 'middle of the stream,' as applied to a navigable river, is the same as the middle of the channel of such stream, and in that sense the terms are used in the treaty of peace between Great Britain, France, and Spain, concluded at Paris in 1763. By the language, ‘a line drawn along the middle of the river Mississippi from its source to the river Iberville,' as there used, is meant along the middle of the channel of the river Mississippi."

This judgment related to navigable rivers. But we are of opinion that, on occasion, the principle of the thalweg is applicable, in respect of water boundaries, to sounds, bays, straits, gulfs, estuaries and other arms of the sea.

As to boundary lakes and landlocked seas, where there is no necessary track of navigation, the line of demarcation is drawn in the middle, and this is true of narrow straits separating the lands of two different States; but whenever there is a deep water sailing channel therein, it is thought by the publicists that the rule of the thalweg applies. 1 Martens (F. de), 2d ed. 134; Hall; § 38; Bluntschli, 5th ed. §§ 298, 299; 1 Oppenheim, 254, 255.

Thus Martens writes: "What we have said in regard to rivers and lakes is equally applicable to the straits or gulfs of the sea, especially those which do not exceed the ordinary width of rivers or double the distance that a cannon can carry."

So Pradier Fodéré says (Vol. II, p. 202), that as to lakes, "in communciation with or connected with the sea, they ought to be considered under the same rules as international rivers." The same view is confirmed by decisions of this court and of many arbitral tribunals.

In Devoe Manufacturing Company, 108 U. S. 401, the question at issue was in regard to the boundary line between New York and New Jersey under an agreement between the two

States. The jurisdiction of the State of New Jersey was claimed "to extend down to the bay of New York, and to the channel midway of said bay," and this court sustained the claim. See Hamburg American Steamship Company v. Grube, 196 U. S. 407.

In the San Juan Water Boundary controversy between the United States and Great Britain, Emperor William I gave the award in favor of the United States, October 21, 1871, by deciding "that the boundary line between the territory of Her Brittanic Majesty and the United States should be drawn through the Haro Channel;" and it is apparent that the decision was based on the deep channel theory as applicable to sounds and arms of the sea, such as the straits of San Juan de Fuca; indeed in a subsequent definition of the boundary, signed by the Secretary of State, the British Minister, and the British representative, the boundary line was said to be prolonged until "it reaches the center of the fairway of the Straits of San Juan de Fuca." The fairway was the equivalent of the thalweg.

Again, in fixing the boundary line of the Detroit river, under the sixth and seventh articles of the treaty of Ghent, the deep water channel was adopted, giving Belle Isle to the United States as lying north of that channel.

So in the Alaskan Boundary case, the majority of the arbitration tribunal, made up of Baron Alverstone, Lord Chief Justice of England, Mr. Secretary Root, and Senators Lodge and Turner, held that the middle of the Portland Channel was the proper boundary line and included Wales Island, to the north of which the channel passed. This sustained the American contention in regard to the thalweg and the island lying south of it.

But counsel contend that the rule "as to the flow of the midchannel or thalweg of the river Iberville (now known as Manchac) through the east, through Lakes Maurepas and Pontchartrain expires by its own limitation when such midchannel reaches Lake Borgne, which in contemplation of the rule is the

This

open sea, and part of the waters of the Gulf of Mexico. contention is inconsistent, as matter of fact, with the allegation of the cross bill that "the Mississippi Sound was recognized as a body of water six leagues wide, wholly within the State of Mississippi from Lake Borgne to the Alabama line, separate and distinct from the Gulf of Mexico," and with Mississippi's Exbibit Map A presenting her claim, while the record shows that the strip of water, part of Lake Borgne and Mississippi Sound, is not an open sea but a very shallow arm of the sea, having outside of the deep water channel an inconsiderable depth.

The maritime belt is that part of the sea which, in contradistinction to the open sea, is under the sway of the riparian States, which can exclusively reserve the fishery within their respective maritime belts for their own citizens, whether fish, or pearls, or amber, or other products of the sea. See Manchester v. Massachusetts, 139 U. S. 240; McCready v. Virginia, 94 U. S. 391.

In Manchester v. Massachusetts, the court said: "We think it must be regarded as established that, as between nations, the minimum limit of the territorial jurisdiction of a nation over tide waters is a marine league from its coast; that bays wholly within its territory not exceeding two marine leagues in width at the mouth are within this limit; and that included in this territorial jurisdiction is the right of control over fisheries, whether the fish be migratory, free swimming fish, or free moving fish, or fish attached to or embedded in the soil. The open sea within this limit is, of course, subject to the common right of navigation; and all governments, for the purpose of self protection in time of war or for the prevention of frauds on its revenue, exercise an authority beyond this limit."

Questions as to the breadth of the maritime belt or the extent of the sway of the riparian States require no special consideration here. The facts render such discussion unnecessary.

Islands formed by alluvion were held by Lord Stowell, in respect of certain mud islands at the mouth of the Mississippi,

202 U.S.

Opinion of the Court.

to be "natural appendages of the coast on which they border, and from which indeed they are formed." The Anna (1805), 5 C. Rob. 373.

As to these particular waters, the observations of Mr. Hall, 4th ed. p. 129, are in point: "Off the coast of Florida, among the Bahamas, along the shores of Cuba, and in the Pacific, are to be found groups of numerous islands and islets rising out of vast banks, which are covered with very shoal water, and either form a line more or less parallel with land or compose systems of their own, in both cases enclosing considerable sheets of water, which are sometimes also shoal and sometimes relatively deep. The entrance to these interior bays or lagoons may be wide in breadth of surface water, but it is narrow in navigable water.

He then states the specific case of the Archipiélago de los Canarios on the coast of Guba, and says: "In cases of this sort the question whether the interior waters are, or are not, lakes enclosed within the territory, must always depend upon the depth upon the banks, and the width of the entrances. Each must be judged upon its own merits. But in the instance cited, there can be little doubt that the whole Archipiélago de los Canarios is a mere salt water lake, and that the boundary of the land of Cuba runs along the exterior edge of the bank."

In such circumstances as exist in the present case, we perceive no reason for declining to apply the rule of the thalweg in determining the boundary.

4. Moreover, it appears from the record that the various departments of the United States Government have recognized Louisiana's ownership of the disputed area; that Louisiana has always asserted it; and that Mississippi has repeatedly recognized it, and not until recently has disputed it.

The question is one of boundary, and this court has many times held that, as between the States of the Union, long acquiescence in the assertion of a particular boundary and the exercise of dominion and sovereignty over the territory within it, should be accepted as conclusive, whatever the international