Multi-criterion water quality analysis of the Danube River in Serbia: A visualisation approach

River quality analysis is an important activity which, in Serbia, has been performed using the Serbian Water Quality Index (SWQI). This is a measure based on a weighted aggregation of 10 water quality parameters. In this work, alternative methods drawing on visualisation approaches used in multi-criterion decision analysis are applied to the problem of evaluating river quality in the Danube. Two methods are considered: one which constructs a graph using the dominance relation combined with a further multi-criterion ranking method, average rank, and the other in which the dimensionality of the data is reduced using PCA for visualisation. Results for data collected in 2010 are analysed and compared with the corresponding SWQI values for the river in that year, and we find that by employing these methods it is possible to reveal more information within the data than is possible by using SWQI alone. •Preference information within water quality indicators (WQIs) is often disregarded.•Multi-criteria visualisation of WQIs reveals greater insight into river quality.•Applying ranking information to PCA-based visualisations enhances their usefulness.•Temporal information within WQIs has an important affect on river quality.