MOBILE BAY. The estuary of the Alabama and Tombigbee Rivers (whose waters after their junction form the Mobile and Tensas Rivers), running into the Gulf of Mexico, through the southwestern portion of the State of Alabama (Map: Alabama, B 5). It is about 30 miles long and from 10 to 12 miles wide. The island of Dauphin lies west of the entrance, which is defended by Forts Morgan and Gaines, and on the east is Mobile Point, the station of a lighthouse with a revolving light. The bay has also an outlet on the southwest through Grant's Pass, communicating with Mississippi Sound, used by steamers of light draught, and the regular course of the Mobile and New Orleans steamers. The harbor, once quite shallow, has been improved by the United States Government; ships drawing over 23 feet of water can now enter the lower bay, and vessels drawing 17 to 23 feet can pass through the channel to the wharves of Mobile. See Mobile Bay, Battle of.