Three seafarers on the Cal Mac vessel, MV Isle of Lewis, are confirmed to have coronavirus.
The first positive result from a Cal Mac crew member was on Saturday. The individual had left the vessel on Wednesday.
Two others also showed symptoms and took tests.
MV Isle of Lewis was covering the Stornoway -
The ferry is now in Oban for a deep clean.
Meanwhile, the health board said a cluster of three positive coronavirus cases has been identified in the islands.
Robert Morrison, operations director for Cal Mac, said: "Three crew members from the MV Isle of Lewis have received positive tests for Covid-
"In line with strict procedures, the vessel was returned from Barra to Oban without passengers and will undergo a deep clean by a specialist company.
"A relief crew is being brought in to operate the vessel once it returns safely to service."
He added: "Cal Mac crew work in strict bubbles in order to protect passengers and colleagues but anyone concerned about potential symptoms should check the NHS Inform website.”
Sunday morning’s sailing was cancelled as a result. The Lewis will not operate the Barra service today.
Instead, MV Isle of Arran will call into Castlebay on route to South Uist. She departs Oban at 3pm and arrives Lochboisdale at 11pm. Space is very limited on the vessel with no guarantee that all vehicles will be transported.
The vessel sailed from Castlebay to Oban without passengers or vehicles to "eliminate any possible risk to members of the public," said Cal Mac.
Cal Mac confirmed a replacement crew will provided for the seafarers who were in close contact with crew members who tested positive.
Passengers on Sunday morning were advised to divert on an island-
Ferry out of service after crew members test positive for covid
8 November 2020