N.Y. Nav. Law § 80

§ 80. Three feet depth to be maintained. Whenever a municipal\ncorporation shall divert or cause to be diverted the water, or a portion\nthereof, of a fresh water stream or streams outside the limits of an\nincorporated city flowing into a tidewater creek or estuary which\ntidewater creek or estuary before such diversion was navigable for\nvessels of twenty or more tons burden, it shall be the duty of the\ncorporation so diverting or causing to be diverted such stream or\nstreams of fresh water to keep said navigable tidewater creek or estuary\ndeepened to the depth of at least three feet at low water mark from its\nmouth to the head of tidewater for the full natural width of said creek,\nand to maintain such navigable depth of water at all times, but in the\ncounty of Nassau it shall not be compulsory to maintain such depth to\nany greater width than fifty feet.\n