That's an isthmus. Loot at a map of Panama.
An isthmus.
An isthmus is a narrow strip of land with water on either side that connects two larger land areas. It serves as a link between two bodies of land, such as connecting two continents or separating two bodies of water.
A "peninsular" or if it connecting two larger areas an "isthmus".
An isthmus is a narrow strip of land bordered on both sides by water, connecting two larger bodies of land
river
If there is a river connecting the waters, then yes.
straight
isthmus.
strait
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.