As the naval force of the Seto Inland Sea, consisting of the navies of the Mori Clan, the Kobayakawa Clan, and the Murakami Clan, attempted to deliver provisions to Ishiyama Hongan-ji Temple, which had been surrounded by the army of Nobunaga ODA, they were confronted by the naval force of the Oda clan, who tried to block them, and clashed with them at the mouth of the Kizu-kawa River in the Osaka Bay.
織田信長軍の攻囲を受ける石山本願寺への兵糧搬入を目的とした毛利水軍・小早川水軍・村上水軍を中心とする瀬戸内の水軍戦力と、それを阻止せんとする織田方の水軍戦力が大阪湾木津川(大阪府)河口で激突した。