The Black Lütschine from the Grindelwald valley and the White Lütschine from the Lauterbrunnen valley are the two source rivers of the river Lütschine, which flows near Bönigen into the lake of Brienz. The name Black Lütschine is due to its dark colour. It is mainly visible down in the valley where it confluences with the whit milky glacier river from the Lower Grindelwald Glacier (called as well «White Lütschine»). The secret of the black colour comes from the geology: the river crosses black shales which releases small particles. This fine material is the reason for the characteristic dark colour of the water.