This research focuses on the impact of extreme low river discharges, meaning discharges below 1200 m2/s at Lobith. In 2018 extreme low river discharges in the river Rhine led to congestions in the main Dutch part, called the river Waal. The river Waal is an important river for inland navigation, but during low discharges the vessel draught reduces and consequently the transported cargo volume per shipment reduces. To compensate the loss of transport volume, the total number of shipments increases, leading to an increased traffic intensity on the river Waal.  The purpose of this study was to investigate the effects of extreme low discharges on the traffic flow and traffic capacity in the river Waal. The study consisted of two elements: a study combining fleet data and hydraulic information and a traffic simulation study. During this research IVS90 data was used as the source for inland waterway transport data. Based on literature and previous river Waal studies the river section between the Pannerdensche Kop and the Maas-Waal canal was selected as the river section to investigate in more detail. Multi-beam measurements in combination with water level data were used to generate cross-sectional profiles in order to carry out the simulations. The cross-sectional profiles were highly variable. From these cross-sectional profiles the navigable river width was determined. It was found that a river depth of 2.80 m was no longer available at all cross-sections from a discharge of 900 m2/s and lower. Therefore, the navigable width was determined at a river depth of 2.0 m for the discharges 1020, 900, 800, 700 and 600 m2/s. Also, it was found that with reducing discharge the navigable width of the cross-sections reduced.   The fleet composition was determined in detail for four weeks representing the drought of 2018. These four weeks in 2018 represented weeks with average discharges around 1020(2x), 800 and 700 m2/s. The river Waal fleet composition was determined based on the Rijkswaterstaat vessel classification system (RWS-class) and categorised in three groups: coupled units (all RWS-classes with index C), push-tow units (all RWS-classes with index B) and motorised vessels (all RWS-classes with index M). It was found that the number of passages by coupled units and push-tow units was effected largely during the drought of 2018. The number of passages by push-tow units reduced significantly from October 2018 as the discharge dropped below 1500 m2/s and the number of passages remained low until the discharge raise above the 1020 m2/s at the end of 2018. The number of passages by coupled units increased already before the discharge reached the 1020 m2/s limit and continued to increase throughout the period of drought. The number of passages by coupled units started to decline only after the discharge rose above the 1020 m2/s again. Even though the daily average number of passages increased during the drought of 2018, the total transported cargo volume per day decreased. There was a strong relationship between discharges below 1200 m2/s and the transported cargo volume per day.  Within this study special attention was given to the occurrence of congestion in the river Waal. The occurrence of congestion was investigated using the traffic simulation model SIMDAS. As indicators for congestion a fluency and safety limit of 8% was used to evaluate the simulated traffic, as well as simulations of the traffic flow. As safety parameter the penetration of the safety margin of a vessel in percentage of the total number of vessel interactions was used. While the percentage of the number of vessels that need to reduce their speed fully during their passages was used as the fluency parameter. With SIMDAS also the impact of increased traffic intensity and reduced navigable width were analyzed. The simulation results showed that the reduced navigable width had more impact on the delay time, the fluency parameter and the safety parameter than the increase of the daily intensity. During the simulations large congestions occurred for discharges of 800 m2/s and lower, but small harmonically moving congestions already occurred for a discharge of 1020 m2/s. Harmonically moving congestions, meaning seven or more vessels traveling behind one larger or slower vessel while awaiting room to overtake, were observed in the traffic simulations. Permanent congestions with ten or more vessels were observed in the simulation of the river width with a 800 m2/s discharge. The data analysis and the traffic simulations clearly showed the effects of the extreme low discharges on the traffic flow and traffic capacity. The conclusion of this study is that the traffic capacity of the river Waal is at its limit at discharges of 800 m2/s and lower.  This study made also clear the need for correct fleet data and river bed levels. The limited available fleet data reduced the accuracy of the results. The river bed should be monitored regularly in order to know the actual water depth particularly during low discharges. Furthermore, it is recommended that highly variable river profiles are implemented in the traffic simulation model SIMDAS to improve the simulation of the vessel's sailing trajectories. Also, the validation of the vessel trajectories in SIMDAS with AIS data is recommended in order to evaluate the traffic intensity on the traffic lanes in the river.