A large inland body of water is called a lake.
Lake
Lake.
A freshwater lake.
Islands
Islands
An island is a body of land completely surrounded by water.
Ocean: A vast body of saltwater that covers the majority of the Earth's surface. Lake: An inland body of freshwater surrounded by land. River: A flowing body of freshwater that moves in one direction towards a larger body of water. Wetland: An area of land that is saturated with water, such as marshes, swamps, and bogs.
An Island
Land surrounded by water is an island . You are describing a peninsula.
A peninsula is a body of land surrounded by water except for one connection to land. An isthmus is a narrow strip of land surrounded by water on both sides, but connected to land on both ends.
A body of body surrounded by land is can be referred to by several different names. A lake - Generally a freshwater body of water that is fairly sizable. A sea - Usually a saltwater body of water with no outlet to the ocean (such as the Dead Sea). A pond - A smaller body of water than a lake. Usually man made. Usually the preferred term for a large freshwater body of water would be "lake" and a large body of salt water would be a "sea".
An island. Or if your really picky, a floating rock.