An isthmus.
That's an isthmus. Loot at a map of Panama.
A "peninsular" or if it connecting two larger areas an "isthmus".
river
If there is a river connecting the waters, then yes.
strait
isthmus.
straight
A 'strait' is a narrow body of water connecting two larger areas of water or connecting two seas.
It is a narrow strip of land connecting two larger land areas.
A narrow strip of land connecting two larger land areas usually with waterforms on either side.
Yes, an ismus is a narrow strip of land between two water bodies that connects two larger areas of land.