The one 'near' Decatur is not public, but we dive it a few times a year. The owner is nice and will let us diver it. not much to see in it but a pile of tires though. but it's one of the clearest quarries I've been in.
Madison Quarry is open until the end of October. check
Better Diver Madison Quarry
It's open on weekends. Cost is $20 bucks (cash reccomended as I don't think they have a credit card machine on site). It's closing down soon because the lease is only until the end of October. Hopefully we'll hear some good news on that soon though.
The Madison Quarry will be about 72f to 76f right about now with little or no thermocline to a depth of about 45 feet max. Nice and warm still. They have a couple docks set up for entry and several items sunk. A firetruck, s-10 pickup, several runabout boats, 3 houseboat size boats, assorted tubes, a F4 fighter, a Minuteman Missile, a small bridge span, lots of display stuff from the local NASA museum that the dont use anymore and was sunk. Lines are strung from most items to other items. It's a great place to dive and nice and convienent.
They have some rental equipment and tanks onsite, but it's advised to reserve them first as they might already be all in use (by rental or a class). If so there are a couple other dive shops around that have gear/tanks also. They have airfills on site and I think his air is o2 clean now and might have nitrox fills. Most folks just bring what tanks they'll need so that they don't have to drive back up top of the quarry and wait for a fill though.
The quarry up outside Nashville (Martha's Quarry) is closed right now. So is Glencoe Quarry (DiveLand) near gasden. Alabama Bluewater (just south of Birmingham) is open also. There is another quarry outside of Moulton (about 1/2 hour west of Decatur) that may or may not be open. I haven't heard a report on it all year. So not sure.