Riparian trees and large woody debris (LWD) have become recently the subject of research also in the Czech Republic. The presented paper deals with the mapping and measurement of LWD in the riparian zone of the Dyje River upstream of the water reservoir Znojmo. The main objective of the study was to find out the number, dimensions, volume and spatial distribution of individual LWD pieces as well as LWD accumulations. Mapping of the LWD was initiated by the hazardous situation during the flood in March 2006, when the large amount of woody debris was transported to Znojmo reservoir and threatened its earth dam. Mapping in the 3.4 km long stretch of the Dyje River showed the presence of 1,108 pieces of LWD which represents 215 m3 of tree biomass. Altogether 110 wood jams are present which are located within the riparian zone. Transport potential of the river during floods is high, however, highly sinuous valley morphology and well developed riparian vegetation inhibit the transport of LWD for long distances.