Entropy theory was applied to generate standards for the assessment of the optimal water quality monitoring network. The entropy theory considers the trans-information among both locations where water quality monitoring facilities are installed and locations without such facilities. Therefore, the theory can support the establishment of the water quality monitoring network by reducing the uncertainty on the basis of information produced by the network. This study has been applied to Geum river

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... ystem to evaluate if the current network for each water quality item is in proper level. In the results, The order of significant sites is different for each water quality item. It is because each water quality item has different influence factors. The pattern of information increase from an additional site is different from each water quality items. For some items (BOD, pH, T-N) the total information stagnates after a certain number of sites, however, for others (COD, SS, T-P) it still increases almost linearly as a new site is added. This means that the current monitoring network has insufficient number of sites for some water quality items.