Diving in Bahraini waters is ridiculous. First of all, the waters are very saline and shallow. Local authorities turn every blind eye they have towards legal & illegal dredging, dumping, over fishing & everything else that destroys anything worth diving on.
The only thing worth diving on is a dying reef 2 hours north of the country & even then, you would be better off at home since even this site (Bulthama) is not worth a 4 hour round trip.
Bahrain is a good place for new divers to train & get experience however. Harsh conditions such as extreme heat & humidity during the summer, lack of any reasonable visibility, returning to the few dive sites over & over, unreliable weather forecasts, higher than anticipated waves & currents all mean that by the time your done diving for 2 months, you can handle any situation an open water or advanced open water diver is licensed to encounter (other than extreme cold). And there is no such thing as shore diving.
That being said, the best dive shops I can recommend are Eco Dive Centre (Wahid, 3944 4799 / Salman, 3933 3123) & Aqua Hobbies (Ahmed, 1729 3231). These are the only 2 professional divers I've dived with, although, they cant do anything about the crappy dive sites either.
There are several other dive operators around, but they are all small ticket places that are little more than a man on a boat.
& for the love of all things holly, stay away from the highly advertised Aquatique. With all that your up against diving here, their exorborant prices, bad attitude & their anti-customer customer service are the last thing you need. I made the mistake of diving with these guys, four times.
This of course, doesn't include the Bahrain Yacht Club, which is by far the best dive operator on the island.
All in all, your better off going to the desert for some tranquility & a good bbq than dealing with the tragic hell that is diving in Bahrain.