The Hudson River is a river that flows from north to south primarily through eastern New York in the United States. The river originates in the Adirondack Mountains of Upstate New York, flows through the Hudson Valley, and eventually drains into the Atlantic Ocean, between New York City and Jersey City. The river serves as a political boundary between the states of New Jersey and New York, and further north between New York counties. The lower half of the river is a tidal estuary occupying the Hudson Fjord, which formed during the most recent period of North American glaciation, estimated at 26,000 to 13,300 years ago. Tidal waters influence the Hudson's flow from as far north as Troy.