Environmental measurement of Dokai Bay surrounded by a Japanese leading heavy and chemical industrial area is evaluated as one of the success instances from the heavy industrial pollution which degraded the bay's ecosystem to be called "the dead sea". After the restoration, the bay newly encounters the water pollution including man-made chemical contamination and eutrophication. We start the comprehensive investigation and research reviving the rich aquatic ecosystem. In this paper, we reported the outline of condensed and typical water pollution history of the bay and our present results and plan of new research improving the bay's ecosystem.
Dokai Bay, located in the northern part of Kyushu island was once called "the Dead Sea", because no aquatic organisms could live in the bay due to the harmful effects of inflowing untreated industrial waste water. However, after the enforcement of wastewater purification measures, improvement of the aquatic environment, shown not only by chemical analysis but also by restoration of the aquatic ecosystem, was dramatic. The recovery of Dokai Bay is cited as one of the most successful instances of water purification, reviving a terribly polluted and damaged aquatic environment in a short period. Therefore, this dramatic improvement of the aquatic environment is called the "Dokai Bay Success Story". The present day, however, the bay suffers from other type of water pollution by man-made chemicals(Kadokami, Jinya, Iwamura and Tanizaki, 1998; Jinya, Kadokami, Iwamura, Hamada, Yamada and Yanagi, 2001) and/or eutrophication by nitrogen and phosphorus (Yamada, 1982; Yamada, and Tokuzaki, 1982). as well as enclosed coastal areas located near the big cities in the world(Takeoka, 1996; Kemp, and Boynto, 1997). Besides such water quality issues, the habitats for aquatic animals are left poor by the concrete quay covered about 99.9% of coastal line of the bay.