About 175th Street in Fort Washington Park
This is not an official beach but unsigned access to the Hudson River in a semi-protected area.
There are no lifeguards.
There is no parking.
There are bathrooms that may not be open. There used to be portable toilets here.
The only way to get here is to walk, jog, or bike in.
Its a very pretty area. The beach is popular with children and dogs. There are so few sand beaches in Manhattan. You are very close to the Little Red Lighthouse and the George Washington Bridge.
The bottom is sandy as you enter. Not rock or mud as might be expected. At low tide expect to encounter a muddy bottom if you try to stand. At higher tides, standing is not an option unless you are closer in.
As the area creates a bit of a cove, it's kind of sheltered from the Hudson River currents.
If there's wind you may find yourself moved more by the wind than by any current. If the wind is blowing from the south (which is quite typical in summer) you may get whiffs of an offputting smell from the North River Wastewater Treatment plant a little over a mile to the south. As the guy who does the Sisyphus Stones rock stacking thing to the south may be burning some incense, that smell may cover the offputting wastewater treatment plant smell.
If you are outside of the area which makes it a bay or cove you will experience typical Hudson River currents.