Since the 90ties there is, in some areas of Germany, a significant rise of the groundwater table at regional scale. The cause for that rise is connected with some short periods of increased precipitation and, in particular, with a reduction in the domestic and industrial use of the groundwater. On the latter point a pronounced effect stems from the closure of open-cast lignite mines in central Germany. After decades of artificially lowered groundwater table, the flooding of the vacated open pits causes a large-scale rise of the groundwater table with significant geotechnical repercussions. Another area, subject to groundwater rise due to increased precipitation as mentioned above, is the Ried region in the State of Hesse. In this publication some selected soils are investigated on the change of their mechanical properties in connection with the rise of the groundwater. Oedometer tests revealed a sagging mechanism which, in its rate and amount turned out to be temperature dependent. Under the scanning electron microscope it was found that the stability of the soil skeleton is intrinsically connected with the cementation of the grains and the formation of aggregates in the soil. Inundation in the rising groundwater causes a dissolution of the cementation which, in turn, leads to grain collapse and the onset of sagging. The mechanism is that sensitive that even a marginal increase in the water content may be sufficient to trigger the sequence of these events.