Außenalster (pronounced [ˈaʊsn̩ˌʔalstɐ] (listen)) or Outer Alster Lake is the larger one of two artificial lakes, which are formed by the Alster River and are both located within the city limits of Hamburg, Germany. The other „lake“ is the Binnenalster. The Außenalster and its shores are used by the inhabitants of Hamburg for many sport and recreational purposes, such as sailing and rowing. From Wikipedia
