This paper describes the reconstruction of the geomorphologic and landscape effects of the most catastrophic flood owing to dam failure within the territory of today's Czech Republic, namely, the Bílá Desná dam failure of 1916. Because of the realisation of the significant later transformation of the Bílá Desná river catchment almost 100 years after the flood event, the field research performed during the summer and fall of 2013 had to be supported by extensive research in regional archives for documentary data. Various data types and sources (such as court investigation notes, investigation reports for insurance companies, old maps, and old photos, as well as video and recorded testimonies of survivors) were used to reconstruct the magnitude (discharge, flood wave extent) of the flood and its effects on the channel morphology and landscape. According to the reconstruction of the dam failure, which was caused by the internal erosion of the dam, the calculated peak discharge ranged between 418.2 and 1491.7 m3s− 1 and therefore exceeded the mean flow rate of the Bílá Desná River by more than 850 times. The river channel immediately upstream and downstream of the dam reclaimed its former meandering pattern with higher sinuosity, and new gravel point bars and irregular bars have been formed. Moreover, the river channel immediately below the dam shifted by up to 30 m following the flood wave. The most significant flood impacts were apparent in the village of Desná, where the flood wave, together with transported boulders (up to 2 m in diametre) and logs from sawmills situated upstream, killed 62 inhabitants and damaged or destroyed 101 buildings. The reconstructed flood wave in the towns of Desná and Tanvald exceeded the bankfull water level twice, with a width ranging between ~ 50 and 250 m in contrast to the average channel width of a few metres.