By late May, the annual spring meltwater from the Alps meant many Bavarian rivers were already at a high water level.
On 22 May the rainstorm "Quartus" hit the northern Alps, bringing an additional 180 litres/m2, causing the Ammersee and the Amper and Isar rivers to expand and flood large areas.
These flooded areas expanded quickly covering parts of the Oberallgäu on the river Iller.
The water level of the Isar, which flows through Munich, was lowered by the Sylvensteinspeicher reservoir near Bad Tölz.
In the Vorarlberg area the Rhine flood affected Lake Constance damaging Hard and Bregenz.