Trettachtal (Trettach Valley) is one of Oberstdorf’s valleys, which are characterised by glacial drift from the latest ice age. The valley glaciers from the large side valleys gradually crept south, forming the scenery that is visible today. As the glaciers receded, watercourses formed the current valleys, among them the beautiful Trettachtal.

The Trettach stream originates south of Oberstdorf near the Trettachspitze and is about 14 km long. North of Oberstdorf, the Trettach merges with the Breitach to form the river Iller.