The status of water quantity in the inundation area around Kopački Rit is indicated by water levels at the nearby hydrological stations on the Drava and Danube Rivers. The status within Kopački Rit itself and the status at individual stations is interdependent. The assessment of the Kopački Rit behaviour was enabled by a relatively short measurement of water levels in Kopačko Jezero (lake) in the period 2001-2003. The analysis of simultaneous daily values of water levels at different locations showed a marked data dispersion in view of average correlation dependencies. It was concluded that the Danube River had a significant impact on the water levels in Kopački Rit and the Drava River. The Danube backwater occurs upstream of Belišće as well. It is noticeable that the water levels at Kopačko Jezero itself significantly depend on the water levels at Apatin, both with regard to its upward and downward trends. A preceding state of increased hu- midity or dryness is also of importance. According to the periodic data (1949-1990 and 1992-1997), a decrease in the characteristic water levels was confirmed in relation to the previous monitoring period, including a further downward trend. The data from the representative station Apatin was used in the calculation of frequency and duration for the new data. A comparison of the derived curves of water level frequency and duration for the successive periods showed a significant decrease in the duration of those water levels that ensure the ecologically critical humidity of the Kopački Rit wetland (81.5 - 83.0 m a.s.l.).