The influence of three waves of the flood in May, June and September 2010 on the water quality in the Goczałkowice reservoir has been studied. For each sample, levels of 22 indicators of water quality were determined. Most amongst all indicators were measured 42–48 times per year. The data were statistically analyzed. It has been shown that cluster analysis of standardized indicators of water quality may be used to distinguish clearly separated groups of measurements from the period of floods and periods beyond. Distribution’ diversities in the water quality indicators were tested separately, and were compared including the following periods: during and beyond floods in 2010, during the floods in 2010 and 1997, as well as during the floods, and month-corresponding multi-year period 1994–2009. It has been shown that flood characteristically affects the distribution of the indicators of water quality – regardless of season, and also the passage of time
