An anchor unexpectedly dropped from one of the largest vessels in the BC Ferries fleet this morning, while the ship was mid-voyage.

BC Ferries spokeswoman Debra Marshall says no passengers were hurt and the Spirit of British Columbia was undamaged when one of the ship's two anchors let go.

The vessel, which can carry 2,100 passengers, was making its first run of the day from Vancouver Island to Tsawwassen on the B.C. mainland.

The incident occurred just east of Active Pass, a narrow passage known for its hairpin turn and challenging currents between Galiano Island and Mayne Island in Georgia Strait.

It's not known what caused the anchor to tumble into the water but Marshall says the ship was halted for about an hour as crews retrieved it.

The incident comes just over two weeks after a small engine-room fire aboard the vessel's sister ship, the Spirit of Vancouver Island, disrupted Thanksgiving weekend holiday plans for thousands of travellers.