To investigate the effect of woody vegetation and especially their roots on levee stability, a literature research was done, the rootstock of a withe willow (Salix alba) which is located on a levee at the Zaya (NÖ) was excavated and investigated and further root systems of the same species at the Danube in Hainburg (NÖ) were explored. Both literature research and the results of the excavation attest to the fact that roots in levees occur predominantly in the soil surface. Especially fine roots are restricted to the humus and less compact surface area. The direction of root growth appears to be increasingly horizontal and the number of roots are elevated on the lower slope of the rootstock compared to those on the upper slope. Root development is highly influenced by soil structure and the availability of water. Investigations at the Zaya and in Hainburg also venture the hypothesis that horizontal roots near the river grow with the flow direction of the water. From todays point of view, shrubby willows grown from brush-mattresses could be a suitable vegetation for levees because they build dense, soil stabilizing root systems without penetrating too deep into the levee itself. Besides that, they have thin, flexible trunks which protect the levee surface during overtopping. Because root characteristics depend that much on tree species and the construction of the levee, the effects of roots on the stability of the levee are, in a sense, able to be influenced. This proves that a, in soil bioengineering approved and successfully used vegetation form, like shrubby willows grown from brush-mattresses, can, on an accurate constructed levee, improve its stability.