Delta SHU size: ~ 197 sq mi / 125,778 acres. The Mobile River basin (~43,679 square miles) drains into the Mobile-Tensaw River delta. The Mobile River basin boundary is the black dotted line and the Mobile-Tensasw River delta SHU is the red area on the index map to the right. The Mobile River basin's headwaters begin in Missississippi, Tennessee, and Georgia, flow into Alabama, and eventually reach the Mobile-Tensaw River delta and empty into the Gulf of Mexico.