East River

There is nothing stopping a developer from purchasing an area of land under the water. That is how lower Manhattan was formed. They purchased everything below the sea level dirt cheap, and then tossed rocks into to it, to cause the land to appear as if it actually rise. In fact City Hall in Manhattan was built via lottery winnings.

Now with various protections of the wildlife, marine-life, and over all health of environment would place concerns in terms of actually doing this in the modern world. Again could be done in terms of legality of owning property.

Another issue would be a reversal of sea-travel. Little do you know many ports and sea bearing cargo is faster, cheaper, and better for the economy. Then of course is the beauty of the Hudson River Valley and how such damns would cause changes unwanted.