Great Morava

The Great Morava begins at the confluence of the South Morava and the West Morava, located near the village of Stalać, a major railway junction in Central Serbia. From there to its confluence with the Danube northeast of the city of Smederevo, the Velika Morava is 185 km long. With its longer branch, the West Morava, it is 493 km long. The South Morava, which represents the natural headwaters of the Morava, used to be longer than the West Morava, but due to the regulations of river bed and melioration, it is shorter nowadays.

At one time the Morava was over 600 km long. Today, the most distant water source in the Morava watershed is the source of the Ibar River, the right and longest tributary of the Zapadna Morava, originating in Montenegro, which gives the Ibar-West Morava-Great Morava river system a length of 550 km, which still makes it the longest waterway in the Balkan Peninsula.

Wikipedia