An estuary is defined as a semi-enclosed body of brackish water
– a mixture of salty and fresh water. So strictly speaking, the
Hudson by Manhattan and northward past the Tappan Zee is
normally an estuary and typically has more ocean water than
river water in the mix. Brackish water can actually work its way
about 70 miles north of NYC to Poughkeepsie in droughts. But
this week, things are different. Due to the melting of this
winter’s heavy snows and also recent rains, the springtime
freshwater flood in the Hudson — the freshet — is fairly large.
An interesting result of this and to a lesser extent the
supermoon spring tide is that salt water is being pushed out to
sea with a rarely seen ferocity and the Hudson is actually a
RIVER along nearly all of its length, running freshwater at all
depths all the way to the northern part of Manhattan. Freshwater
floats over saltier (denser) water, and the surface waters could
actually be fresh all the way to New York Harbor after ebb
tides. USGS has a nice webpage for