My collegues from the Institute for Water of the Republic of Slovenia (IWRS) are involved in the tasks of the European Topic Centre on Water (ETC/W) of EEA. They have calculated CSI019 (Oxygen consuming substances in rivers) using ENW1: River quality data (Waterbase). CSI019 is one of the core set of indicators, which is available on EEA web site. They have calculated the significant trends in annual total ammonium concentrations by countries using stations that have recorded concentrations for at least 7 of the years in the time series from 1992 to 2006 (Mann-Kendall - Sen`s test method). They found out that Sweden has 35 % of all stations (113) with significant upward trends. They think this is a large proportion, because no other European country included in calculation has so high proportion of stations with upward trends (most countries have less than 5 % of all stations with increasing total ammonium concentrations and an average of European countries is 2 %). They would like to ask why the data for Sweden in Waterbase show so high upward trends in total ammonium? Should they use some other data? Marko Kovačič, ETC/W Rivers Data manager