[en] The Environmental Radiology Monitoring Network, consists in a set of 80 sampling points selected from the eight major Spanish rivers basins; an analysis is carried out of the parameters which indicate the radioactivity levels. The samples are collected and sent for analysis to the Nuclear Application Programme's laboratories of the CEDEX, by the respective Water Boards. The values of Total Alpha, Total Beta, Residual Beta, Tritium and Gamma Spectrometry are determined for all the samples. Every hydraulic year, the results are studied according to basins, and the corresponding technical report is issued. (Author)