Lough Ree, translated to English as King's Lake or King Lake, is a lake in the midlands of Ireland, the second of the three major lakes on the River Shannon. Lough Ree is the second largest lake on the Shannon after Lough Derg. The other two major lakes are Lough Allen to the north, and Lough Derg to the south. There are also several minor lakes along the length of the river. The lake serves as a border between the counties of Longford and Westmeath on the eastern side and County Roscommon in the province of Connacht on the western side. The lake is popular for fishing and boating. The lake supports a small commercial eel fishery and is locally famous for its eels on wheels truck. The town of Athlone is situated at the southern end of the lake, and has a harbour for boats going out on the lake. The small town of Lanesboro is at the northern end of the lake.

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.