Now, although the Commissioners have no reason to doubt that the waters of the upper Hudson are perfectly pure, and that by building a water-tight dam across the river, from this city to the shores of New Jersey, the salt water will be ejected, and the fresh will take its place above the dam, yet we fear, that, in locking vessels up, more or less of the salt water below the dam will follow them, and although the quantity may be comparatively small, the constant repetition of the operation, by the hundreds of vessels going through the locks, both day and night, may, perhaps, be the means of unfitting the water, in a measure at least, for domestic use. 2nd. The project cannot be carried into effect, except by an Act of the Legislature of New Jersey, as well as by this State, and perhaps by the Congress of the United States. If all navigable rivers are common highways, it is a question at least, whether obstructions can be placed in them without interfering with the powers of Congress to regulate the Commerce of the Nation. 3rd. It must be conceded, as the Commissioners think, that the building of the proposed dam would be an obstruction of more or less magnitude to the navigation of the river; for although a vessel may be locked through in 10 or 15 minutes, as asserted by Mr. Seymour, still, if we revert to the great number of vessels passing and repassing the proposed site of the dam, it can hardly be otherwise, but that there would be much detention.