Binnenalster or Inner Alster Lake is one of two artificial lakes within the city limits of Hamburg, Germany, which are formed by the river Alster (the other being the Außenalster). The main annual festival is the Alstervergnügen.The lake has an area of 0.2 square kilometres (2,200,000 sq ft). The word "inner" refers to the old city walls of Hamburg. The Binnenalster was the part of the lake that was "inside" the city walls. The lake was originally created to serve as a reservoir for a mill. The old city walls do not exist, instead two car and train bridges, the Lombardsbrücke and the Kennedybrücke, span the river.