A warning in case you were thinking of doing some laundry in the sea loch to the north of the Dun. Although conceivably it could refer to somewhere similarly named – phonetic attempts in English to name Gaelic places are still pretty confusing 300 years later.
There are several Springs and Fountains of curious Effects [on Lewis]; such as that at Loch-Carlvay, that never whitens Linen, which hath often been try’d by the Inhabitants.
From Martin Martin’s ‘Description of the Western Isles of Scotland’ (second edition of 1716).