The combination of extreme sea levels with increased river flow typically can lead to so-called compound floods. Often these are caused by storms (< 1 d), but climatic events such as El Niño could trigger compound floods over a period of months. We show that the combination of increased sea level and river discharge causes extreme water levels to amplify upstream. Mangrove forests, however, can act as a nature-based flood protection by lowering the extreme water levels coming from the sea.