Abstract
To evaluate the water quality of sea areas in Japan, the public observation data on water quality were collected. And, the index of the water quality, which has obtained from the five factors (COD, TN, TP, DO and coliform group) at 952 observation points by the principal component analysis, was proposed. And, the relative water qualities at the 952 observation points were evaluated with 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. Then, the relationship between the water quality index and physical conditions of bay (bayopening-width, tides, average-bay-depth, etc.) were investigated about 56 bays. Except some bays of very bad water quality, it was found that the water quality becomes good with the increase of bay-opening width.
