Though in most places in Orkney water levels have risen, the first O.S. shows this site as a seperate islet. Perhaps the topographic details of the 1882 map came from a particularly wet time ? The isthmus is matched by many Orcadian sites recorded as being connected by causeways or stepping stones. A few of these have been claimed as crannogs, an exception being the Loch of Wasdale’s comparison to the causewayed island duns of the Western Isles. You must tread carefully in more senses than the literal ;-)
Don’t try and reach it by going around the shore from Via (unless you ave some serious welligogs, when you might just).