Within the plane of the refuge, Grand Bay includes the Southern Pine Hills predominantly north of Interstate 10; the Gulf Coast Flatwoods just south of Interstate 10; and the marsh regions in the southern part of Jackson County.
The map seen to the right is the National Wetlands Inventory Map. It illustrates the vegetation communities at the refuge and in the surrounding lands.
In the northernmost swamps, isolated pockets of freshwater marsh dominate the landscape. Further south, brackish marshes exist where tidal influence is constant. Saline marsh along the coast supports many species of open water ducks and other wildlife.
The gradient effect from the flatwoods to the marsh creates bottomland hardwood swamps that provide feeding and resting habitat for a variety of waterfowl, including mallards, green-winged teal and blue-winged teal.