Great War Island is a river island in Belgrade, capital of Serbia. It is located at the confluence of the Sava and Danube rivers. Though uninhabited, the island is part of the Belgrade City proper, and belongs to the city municipality of Zemun.

The Sava is a river in Central and Southeast Europe, a right-bank and the longest tributary of the Danube. It flows through Slovenia, Croatia and along its border with Bosnia and Herzegovina, and finally through Serbia, feeding into the Danube in its capital, Belgrade. The Sava forms the main northern limit of the Balkan Peninsula, and the southern edge of the Pannonian Plain.