-The wide lower course of a river where it flows into the sea. The water in estuaries is a mixture of fresh water and salt water. -An arm of the sea that extends inland to meet the mouth of a river.
The Hudson interacts strongly with the Atlantic Ocean. Now every river that flows into the ocean has a transition point where it stops being river and starts becoming ocean, but the Hudson does this far more than most. It’s flow is tidal, meaning the direction of the flow changes depending on the tide. This occurs not only at New York City near its mouth but also over 150 miles north to Troy. The Naive American name for the Hudson is Mahicantuck, which literally means “river that flows two ways”. If you spend time along the Hudson’s shore you’ll see this. About an hour after the official high or low mark, the river changes direction. This shift isn’t sudden. Often it will start at one part of the river channel then expand to others. (Experienced Hudson River travelers have seen moments when the river is flowing one direction by the shore and the other in the middle.) The reason the tidal action goes as high as Albany/Troy is because the Hudson flows down a very gradual slope. The vertical movement of the water is so small that even in the Albany area the river bottom is still below sea level. That doesn’t mean the river can’t have strong currents. At certain points the flow can be so strong a paddler will be hard-pressed to go against it, especially when the current and the tide are moving downstream together. This back and forth makes a much different ecosystem than a typical river. Most noticeably, the salt front — defined as the point where the water transitions from fresh to salty — is much higher than other rivers. In the spring when there’s a lot of runoff it’s located around the Tappan Zee area, but during the dryer summer the salt front can go as high as Beacon, just north of the narrow Hudson Highlands. Brackish water systems are actually very productive, especially when you combine them with marshy and mudflat shores. These become breeding grounds for oceanic fish, seeking safe places to deposit their eggs. There are many animals such as crabs bluefish and striped bass that thrive in brackish waters. They’re a unique ecosystem vital for the health of the surrounding marine communities. This is why the Hudson used to support commercial fishing industries; the water was full of fish! When you’re paddling on the river, the tides are especially important. Nobody wants to paddle against the current, and the Hudson’s can be fierce. An outgoing tide means that the current and the tide are running together, which can be especially hard to paddle against. Even when the tide is flowing northward against the current, this can be tricky. So make sure if you’re planning a river trip to consult your tide tables. A poorly planned trip from one location to another and back could end up being against the current both ways! Resources: https://www.dec.ny.gov/lands/4923.html http://life.bio.sunysb.edu/marinebio/fc.1.estuaries.html