The Königssee lake is noted for its clear water and is advertised as the cleanest lake in Germany. For this reason, only electric-powered passenger ships, rowing, and pedal boats have been permitted on the lake since 1909. The lake is very popular with tourists and hikers. In addition, the surrounding sheer rock walls create an echo known for its clarity. On boat tours it has become traditional to stop and play a flugelhorn or trumpet to demonstrate the echo. The echo can be heard to reverberate up to seven times.