Mobile Bay Water?

Is the area of Mobile Bay near the tunnel saltwater, freshwater or a combination of both?

Freshwater (on top) most of the time.
But the salinity may rise a bit in the fall IF we haven't had runoff from upstate,
especially on the bottom where the water is 45 feet deep in many places and probably stays 'salty'.

This link shows the salinity reading (in red) taken from that area (on the surface)...
http://tidesandcurrents.noaa.gov/por...7048_ct_24.png

Yes for the most part. The salinity does vary all the time with seasons, tides, rain up north and such just as Pier#R said. I have been on trips around the causeway and caught largemouth bass, flounder, redfish and trout in the same area. It is always a good idea to keep a stocked tackle box when fishing up there or at least a bunch of shrimp.

Brackish to Fresh depending on river discharge and time of year.

The Causeway and points north, yes: but he was asking specifically about the Mobile River fishery.
Folks in my inshore club, the ACFA fish it year-round for speckled trout and catch them there because the water is so deep it stays saltier on the bottom and the trout don't have to vacate the area like they do in the rest of the delta. They just 'hunker down' until the surface salinity rises again.
i believe it's the baitfish that are actualy there all the time (moving around three dimensionally) and the specks just follow the food source.

Agreed! What #r said!

Thank you. When I have driven through the area, I just assumed it was salt water.