12. The Hudson River Estuary
The lower Hudson is also influenced by salty seawater, which pushes upriver and mixes with freshwater from the watershed. Water bodies in which this happens are called estuaries. The leading edge of dilute seawater entering the Hudson is called the salt front. The front does not move upriver as far as the tides. Salty water often reaches Newburgh in summer, and in droughts it might go as far north as Poughkeepsie. But in spring, or after major rainstorms, fresh water runoff can push the salt front as far south as the Tappan Zee or even Manhattan.