The Shannon River Basin consists of the area containing Ireland's longest river, the River Shannon, and all of its tributaries and lakes. The official Ordnance Survey Ireland length of the Shannon from its Shannon Pot source is 224 miles (360 km) made up of 63.5 miles (102.2 km) tidal water flow and 160.5 miles (258.3 km) freshwater flow.

The River Shannon is the major river on the island of Ireland, and at 360 km in length, is the longest river in the British Isles. It drains the Shannon River Basin, which has an area of 16,900 km2 (6,525 sq mi), – approximately one fifth of the area of Ireland.