Is the East River off Manhattan in New York a true river or is it an estuary of the Atlantic Ocean?

Answer 1

The East River is a tidal strait. It's a strait in that it is a "water passage" between Manhattan and Long Island. Because of tides, it appears to flow like a river. It's not an actual river because it connects on both ends to the ocean. Rivers flow from inland fresh water sources (such as mountain runoff or springs). The Hudson River, on Manhattan's West side, is a true river. It flows downstream from the North. Accordingly, the East River is salt water, the Hudson is fresh water. The East River is not an estuary, though--an estuary is the point of mingling of a river and the ocean. The mouth of the Hudson, though, while perhaps technically forming an estuary, flows around various islands and is channeled to the point that the distinction isn't worth making, as long as you ignore Spuyten Duyvil. You could say the East River is associated with an estuary, but it isn't one itself. One other thing: while the Hudson River does carry fresh water from upstate, the salt water from the Atlantic mingles upstream as far as Poughkeepsie, depending on tides, so it's pretty salty when it hits Manhattan.