However, these two straits do not directly lead to the open sea, but to the Sasebo Bay (佐世保湾, Sasebo-wan).

West of the Ōmura Bay lies the Nishisonogi Peninsula (西彼杵半島, Nishisonogi-hantō), and to the south is the foot of Mount Kotonoo (琴ノ尾岳, Kotonoo-dake).

Opposite Ōmura city lies the largest island of the bay: Mishima (箕島), where Nagasaki Airport is located.

Along the bay shore lie the following towns, clockwise from the north: Sasebo, Kawatana, Higashisonogi, Ōmura, Isahaya, Nagayo, Togitsu, Nagasaki and Saikai.

[3] Another special inhabitant – sometimes characterised as a living fossil – is the horseshoe crab species Tachypleus tridentatus.