Abstract
To evaluate the water quality of sea areas around Japan, a new water quality index was proposed using the data released by public organizations. First, to make the water quality index of sea areas, principal component analysis was applied for the data at 6008 observation points where the data of TN (total nitrogen), TP (total phosphorus) and COD (chemical oxygen demand) were gathered for four yearsfrom 1999 to 2002, and the first principal component was considered as the comprehensive index of water quality. Next, the water qualities of sea areas around Japan were compared by the water quality index. The evaluation shows that the water qualities are relatively bad in sea areas near the big cities and in large harbors. And it is found that the value of the water quality index in polluted seaareas with organic substances is less than -1. In addition, the water quality ofthe Hakata bay for 20 years (from 1983 to 2002) was shown by using the proposed index, and the change of the water quality due to various developments was investigated.
