Alluvial zones are formed when the water from mountain streams, rivers and lakes comes in contact with the ground. Rivers and streams change their course and sometimes flow over their banks when the water level rises. Therefore, alluvial zones change constantly, as a result of the alternation of flooding and low water, and of erosion and sedimentation. These dynamics generate a mosaic of extremely different environments: water courses, dead channels, sandbars, and levees of dry gravel, herbaceous pioneer formations of bushy or tree-like willows and high, dense, impenetrable forests. Within a small area (0.55% of the national territory), alluvial zones provide a habitat for a multitude of plants and animals.

The federal inventory of alluvial zones of national importance currently comprises 283 sites covering a total area of approximately 226 km² (2015). In the Alps, above the tree line, glacial forelands (zones of glacial retreat) and alpine alluvial plains are to be found. At lower altitudes of the Jura, of the Central Plateau and of the Alps one mainly finds alluvial zones along watercourses, but also in some deltas and along the banks of lakes.

Numerous alluvial zones in the inventory have been transformed by human activities. The Ordinance on the Protection of Alluvial Zones of National Importance was brought into force by the Federal Council on 15 November 1992.