Usually, these kinds of places are not in deep water. They are in areas protected enough for diving without super fast currents, where marine life is sheltered enough to accumulate, and where weather is acceptable.
They are generally similar to a B&B or wilderness cabin/camping retreat in that group meals are provided, in a more casual setting than a “resort”. Rooms are often shared, service is more group oriented and less formal. Sometimes guests perform kitchen duties as part of the package.