The Battle of the Marshes (Arabic: معركة الأهوار, Persian: نبرد نیزارها) was a part of the Iran–Iraq War. After the mostly indecisive Dawn operations in 1983, Iran opened a new, surprise amphibious offensive in the lakes of the Hawizeh Marshes in Iraqi Tigris–Euphrates river system. Iraq heavily used chemical weapons (mustard gas) during the battle.