"The Lütschine is a river in the Bernese Oberland region of Switzerland. The Lütschine proper runs from Zweilütschinen, where its two tribututaries join, to Lake Brienz at Bönigen. The Schwarze Lütschine, or Black Lütschine, flows from Grindelwald to Zweilütschinen. The Weisse Lütschine, or White Lütschine, flows from the Lauterbrunnen Valley to Zweilütschinen. The common stretch of the river has a length of 8.6 kilometres (5.3 mi), whilst the Schwarze Lütschine is 12.3 kilometres (7.6 mi) long and the Weisse Lütschine is 13.1 kilometres (8.1 mi) long.
A story passed on by word of mouth showing friendly banter between villagers that lived on the two rivers is that the people on the Weisse Lütschine said the others 'were so dirty it turned the river black' and the villagers on the Schwarze Lütschine claimed the others 'never even washed so the other tributary remained perfectly white.'" ~ Wikipedia
A modern oberserver standing at Zweilütschinen in winter might note that during the day, the west facing Schwarzer Lütschine valley is dark, shaded and cold, whereas the south facing Weisser Lütschine valley is sunny and light.