Andrew Jackson closed it down in the War of 1812. It would be easier today. Drop one of several bridges and a few barges. Open the spillway and lower the level several feet...
Jackson did it with a single fort and some cannon emplacements. Today, missiles and artillery set in among all the industrial installations lining both sides. They would be hard to spot.
“Drop one of several bridges and a few barges. Open the spillway and lower the level several feet...”
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I can only hope that happening were something I’d lose sleep over. But even then it would be below armed unicorns in full combat gear hitting the beach at Coney Island on my list of things to worry about.