We never dove the AKR lagoon, but heard that it makes a fairly good night dive. The "murk" he is talking about comes from the fact that the lagoon is also part of the channel for AKR, BIBR, and some private boats to get outside the reef. It can get some slight current running through if the waves are up, and that stirs up sediment. When we dropped off the boat for the weight check the first day, I would guess vis was 30'+ with a bunch of divers standing on the bottom stirring up the muck. It depends on how much wave action and rain they have had, but the water can be fairly clear there and there are reportedly alot of interesting critters that reside down there. The underwater light they turn on at night reportedly attracts rays and other larger predators.
AKR also offers shore diving from the back end of the key facing onto the "front porch" dive site. That is the site where they do the dolphin dives, so when the dolphin dives are in progress (usually the same time as the boat diving), there is no shore diving allowed there. Based on what I know of the dolphin dive site, it is a series of large sandy areas with coral ridges in between them. Probably a good place to look for eels, rays, and flounder. Might also be a good area for jawfish and blennies that burrow in sand. We did not do the shore dive, but people we asked about it said it was ok. Certainly not the quality of the Prince Albert or the CoCo View Wall, but still a reasonable quality dive if you are the type to go slow and look carefully for the less visible critters. I have always thought that I would like to do Front Porch as dive without the dolphins there sometime, because I really enjoy laying in the sand observing a coral ridge for shy creatures.