The Mobile-Tensaw Delta lies directly north of Mobile Bay in a broad river valley, in parts of Baldwin, Clarke, Mobile, Monroe and Washington counties [1]. It is about 45 miles long and 6 to 16 miles wide, covering roughly 300 square miles, and is a designated National Natural Landmark. The Encyclopedia of Alabama calls it the state’s main remaining natural terrain. See also Mobile Bay.
| Length | About 45 miles |
|---|---|
| Width | 6 to 16 miles |
| Area | About 300 square miles |
| Open water | About 20,000 acres |
| Marsh | About 10,000 acres |
| Swamp | More than 70,000 acres |
| Bottomland forest | More than 85,000 acres |
| Preserved land | 185,500 contiguous acres |
Habitats and species
The delta includes open water, marsh, swamp and bottomland forest. It supports about 500 plant species, 300 birds, 126 fish, 46 mammals, 69 reptiles and 30 amphibians [1]. Many stops on the Alabama Coastal Birding Trail are here. For terms see biodiversity and habitat.
Formation
The valley began forming several million years ago as inland streams merged and flowed south across land once covered by the Gulf of Mexico. About 18,000 years ago Gulf water levels were roughly 400 feet lower. Rising seas flooded the lower stream courses, and Mobile Bay is a flooded former river valley. The Gulf is still rising about 2 millimeters per year [1].
Waterways
Major rivers include the Tombigbee, Alabama, Mobile, Middle, Tensaw, Apalachee, Raft, Spanish and Blakeley. The Mobile River forms the southernmost channel of the Tennessee-Tombigbee Waterway [1].
History
People have lived in the delta for about 5,000 years, and about 700 years ago Mississippian peoples built earthen mounds near Bottle Creek. Later groups included the Alabamas, Mobilians, Taensas, Creeks and Choctaws, and the Tensaw River is named for the Taensa. Pierre Le Moyne d’Iberville founded Fort Louis de la Louisiane and an initial settlement called Mobile in 1702, and his brother Bienville moved it to its present site in 1711. In 1813 Creek attackers struck Fort Mims, and in April 1865 the Battle of Fort Blakeley, the last major Civil War battle, was fought on the delta’s southeastern edge [1]. See Old Mobile Site.
Use and concerns
Today the delta is used mainly for recreation and education, including boating, fishing, hunting and wildlife viewing. Concerns include upstream dams, pollution, invasive species, dredging and development along the U.S. 90 Causeway [1].
Size and rivers
The Mobile-Tensaw River Delta is about 45 miles long and 6 to 16 miles wide, covering about 300 square miles across parts of Baldwin and Mobile counties among others. Nine rivers, including the Mobile, Tensaw and Spanish, make up the system, and 185,500 contiguous acres of federal and state property are preserved. It has been designated a National Natural Landmark.[2]
Biodiversity
The article calls the region home to some of the most diverse wildlife in Alabama and the entire United States, with about 500 plants, 300 birds, 126 fishes, 46 mammals, 69 reptiles and 30 amphibians.[2]
People and uses
Mississippian-period peoples built earthen mounds beside Bottle Creek and the Tensaw River about 700 years ago. Primary uses today are boating, fishing, hunting, wildlife observation and the study of wetland ecology.[2]
FAQs
Where is the Mobile-Tensaw Delta? North of Mobile Bay in southwest Alabama.
How big is it? About 300 square miles.
Is it protected? It is a National Natural Landmark, and 185,500 acres of federal and state land are preserved.
Sources
More in Ecology
Key facts
- About 300 square miles1
Quick checkHow big is the Mobile-Tensaw Delta?Show answer
About 45 miles long and 6 to 16 miles wide, roughly 300 square miles.
Sources
- Encyclopedia of Alabama. Mobile-Tensaw Delta. n.d. (accessed 2026-11-10)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 10, 2026Researched and drafted with AI assistanceReport an issue