Salt, fresh, or both? The Hudson estuary is tidal, and seawater can travel far to the north. This presents a challenge to fish. While some fish like hogchokers are very adaptable to salt, others may be strictly freshwater or saltwater species. Even freshwater has a tiny amount of salt in it (around 20 parts per million). The “salt front” is that point where a measurable amount of sea salt can be detected in the river (around 100 parts per million), though you wouldn’t likely be able to taste it. The ocean has much more salt, about 35,000 parts per million (or 35 parts per thousand). The salt front in the Hudson moves during the course of the year, sometimes reaching as far north as Poughkeepsie.