The definition of an island is that it is land surrounded by water. A peninsula is defined as: A peninsula is a piece of land surrounded by water on the majority of its border, while being connected to a mainland from which it extends. Now, keeping those definitions in mind think about this. Is the Delmarva "peninsula" truly a peninsula? It has the Chesapeake and Delaware Canal separating it from the mainland and Cape Cod has the Cape Cod Canal separating it from the mainland.