This thesis object was the current distribution of Stratiotes aloides, an aquatic macrophyte, and its populations status and endangerment in alluvial areas of the Danube situated in Vienna and Lower Austria. During the vegetating period of the year 2013, population and phenological data has been collected at all plant stands as well as current effects on S.aloides like water level, hydrochemistry, light condition, aquatic vegetation or direct causes of disturbance. Afterwards influences and vitality data have been compared. Stratiotes aloides was found at only four out of nine possible autochtonous locations in the study area, with all four being situated inside protected areas. Two Stratiotes stands were found heavily impacted, only one population could be refered to as in optimum status. For one site only limited data was collectable. Generative propagation was found nowhere within the study area because of no plant stands containing both sexes. However, at three of four stands, vegetative propagation occurred in population sustaining numbers. Hydraulic engineering was found to be the main reason for the species endangerment within the study area, resulting in a loss of hydromorphological dynamics inside the alluvial areas leading to different direct and following impacts on Stratiotes. All populated waters were threatened by long term siltation without the species opportunity to disperse to new sites. At one site a short term siltation threat was detected, which led to direct concurrence for Stratiotes by helophytic species better adapted to later stages within the hydrosere. At another site Stratiotes was maybe affected by the hydrochemical situation. That combined with anthropogenous disturbance and a non-ideal habitat almost led to the stands total extinction. Measures like large scale revitalisation or the artificial creation of plant stands in alternative water bodies are strongly needed to keep Stratiotes aloides existing within the study area.