A lifeline crossing is down to one ferry after a crew member tested positive for Covid-19.
Sailings between Oban and the Isle of Mull on Thursday morning were called off with afternoon journeys also expected to be affected.
A worker on the MV Isle of Mull ferry which serves the Oban to Craignure crossing returned a positive coronavirus test with other members of the crew identified as close contacts.
CalMac urged those who intended to travel to the island as foot passengers on the Thursday morning sailings to not go to Mull as capacity issues could prevent them from returning to Oban.
The ferry operator also warned customers that queues are expected to be longer than usual on the Lochaline and Fishnish crossing, the non-bookable alternative crossing between the mainland and Mull.
Services departing Oban at 7.25am, 9.55am and 12.25pm, and those leaving Craignure at 8.40am, 11.10am, and 1.30pm were all cancelled.
A statement from the ferry operator read: “In line with Covid-19 protocols crew identified as close contacts are being replaced and arrangements have been made for the vessel to be deep cleaned.
“There will be an update at approximately 1.30pm regarding afternoon sailings.”
The MV Coruisk, which carried passengers back and forth from Oban to Mull, was removed from service for days in July after an engine fault putting strain on the already busy crossing.