Bankside groundwater is widely used as drinking water resource and, therefore, contamination has to be avoided. In the European Union groundwater protection is explicit subject to Water Framework Directive. While groundwater pollution may originate from different sources, this study investigated on impacts via flood events. Groundwater was sampled with increasing distance to the river Rhine near Karlsruhe, Germany. Samples were HPLC–MS–MS analyzed for the river contaminant carbamazepine to indicate river water infiltration, giving permanent presence in 250 m distance to the river (14–47 lg Lÿ1). Following a flood event, concentrations of about 16–20 lg Lÿ1 could also be detected in a distance of 750 m to the river. Furthermore, estrogenic activity as determined with the Yeast Estrogen Screen assay was determined to increase up to a 17b-ethinylestradiol equivalent concentration (E-EQ) = 2.9 ng Lÿ1 near the river, while activity was initially measured following the flood with up to E-EQ = 2.6 ng Lÿ1 in 750 m distance. Detections were delayed with increasing distance to the river indicating river water expansion into the aquifer. Flood suspended matter and floodplain soil were fractionated and analyzed for estrogenic activity in parallel giving up to 1.4 ng gÿ1 and up to 0.7 ng gÿ1, respectively. Target analysis focusing on known estrogenic active substances only explained <1% of measured activities. Nevertheless, river water infiltration was shown deep into bankside groundwater, thus, impacting groundwater quality. Therefore, flood events have to be in the focus when aiming for groundwater and drinking water protection as well as for implementation of Water Framework Directive.