This isnt strictly true. Although the Swan and Dartmouth are both protected Lochaline Dive Centre operates a vistor licence, under the auspices of Historic Scotland. The licence allows them to take Sport Divers to both sites but all divers have to be named.
Unfortunately the money ran out so there isnt any work being done on the sites at present and, as mentioned previously, they will both be sandbagged to protect them. Last time I spoke to the guys at Lochaline they said there isnt a great deal to see unless the archaeologists are at work.
Have a look at the
Lochaline Dive Centre visitor scheme, the info is old but the visits are still available
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