NorthLink carried out a routine anchor test at Lerwick harbour last night (Tuesday).
A passenger ferry could be seen anchored in the middle of the harbour, in front of The Lodberry.
NorthLink said it was a planned anchor test, which it needs to carry out every six months or so.
A spokesman said Lerwick Harbour had been informed, as were passengers.
He said it was “standard operating procedure”.
The journey continued as normal after the test was completed.