It flows along the eastern edge of the Black Forest in the German state of Baden-Württemberg (district of Schwarzwald-Baar).

The river is 18.9 kilometres (11.7 mi) long, together with its headstream, the Glasbach.

[2] The Fischbach[3] begins at the confluence of the right-hand Glasbach,[4] also called the Vorderbach, and the left-hand Eschbach[5] which, in turn, is formed by the left-hand Hinterbach and right-hand Reutenbach and then collects the Mittelbach, in the village of Fischbach which belongs to the municipality of Niedereschach.

Hydrographically this may even be considered the main source of the River Neckar, because the Fischbach has a higher streamflow than the Badische Eschach which, in turn, is the larger of the two headstreams, and the Badische Eschach is more powerful than and longer than the young Neckar at their confluence.

The Fischbach flows in a southeasterly direction and merges with the Baden Eschach near Niedereschach.