Lake Brienz is a lake just north of the Alps, in the canton of Berne in Switzerland. It has a length of about 14 kilometres, a width of 2.8 kilometres and a maximum depth of 260 metres. Its area is 29.8 square kilometres, and the surface is 564 metres above the sea-level. It is fed, among others, by the upper reaches of the Aare at its eastern end, the Giessbach at its southern shore from steep, forested and rocky hills of the high Faulhorn and Schwarzhoren more than 2,000 metres above the lake, and by the Lütschine, flowing from the valleys of Grindelwald and Lauterbrunnen, at its south-western corner. It flows out into a further stretch of the Aare at its western end. The culminating point of the lake's drainage basin is the Finsteraarhorn at 4,274 metres above sea level.
The village of Brienz, from which the lake takes its name, lies on the northern shore to its eastern end. In the west, the lake is terminated by the Bödeli, a tongue of land that separates it from neighbouring Lake Thun. The village of Bönigen occupies the lake frontage of the Bödeli, whilst the larger resort town of Interlaken lies on the reach of the Aare between the two lakes.