Ariake Sea

The Ariake Sea is a body of salt water surrounded by Fukuoka, Saga, Nagasaki, and Kumamoto Prefectures, all of which lie on the island of Kyūshū in Japan. It is the largest bay in Kyūshū. Its deepest point is only about 50 m deep, and extreme tides exceed 4 m, covering roughly 1,700 km2. It is used for aquaculture, with nori being a major product. Various species of fauna, including mudskippers, pen shells, and fiddler crabs, live in the Ariake Sea. In autumn, there is red-grass along the sea shore.

Recent years have brought increasing pollution, with resultant red tides. Isahaya Bay is a branch of the Ariake Sea. Across the Amakusa Islands lies the Yatsushiro Sea. There is ongoing land reclamation as evidenced by satellite despite government attempts to dissuade farmers from carrying out the activity.