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This study is undertaken to find the optimal method to make the decision on the degree of water pollution by comparison of K-WQI, KOE-WQI that is made for index with the water quality index and water quality environment standard of the Frame Act on Environment Policy as the result of survey for water quality reality on the major point of the Yeongsan river from 2002 to 2004. The water quality of major rivers has some differences depending on seasons, however, under the water quality standard by the BOD_5 density, most of rivers displayed the water quality level of Ⅱ~Ⅲ grading, and on K-WQI that is classified by indexing for 10 categories of pH, DO, BOD_5, COD, SS, T-N, NH₃-N, NO₃-N, T-P, and E-Coli and classified into 5 groups from 100 points to 40 points, they displayed the score distribution of the first grade in water quality for 85~100 points to the second grade in water quality for 70~84 points. On KOE-WQI that is classified by indexing for 5 categories of pH, DO, BOD_5, COD and T-coli and classified in to 5 groups from 90 points or above for outstanding and 29 points or below for very bad, and the water quality distribution is made ranged from the first grade in water quality for 90 points or more to the third grade in water quality for 69~50 points. In addition, for the contribution of the water quality decline, the Environmental standard has significant dependency on the BOD5 density, with K-WQI contributing in various water quality decline depending on the environment around the river area of BOD5, T-N, NH₃-N, NO₃-N, T-P, and E-Coli, and KOE-WQI acting as the factor contributing to lower the water quality decline by BOD_5, COD, and T-colⅠ. As such, the current water quality environment standard has high dependency on BOD_5 and KOE-WQI excludes some nitrogen and phosphorus that considers the river environment that the grade in water quality is set by some category, and K-WQI reflected well of the ecology environment of rivers with the diversity of the assessment factor as well as to have the low dependency of specific factor to be objective.
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