The Spirit of Kangaroo Island Ferry will be back in service from tomorrow, a week earlier than anticipated.

Sealink says the wet docking essential maintenance tasks the ferry was undergoing have now been finalised.

The ferry was removed from service early this month and sent to Port Lincoln for urgent dry dock maintenance.

With only one ferry left in service, residents and tourists were struggling to find booking spaces to take their vehicles to and from the mainland.

Sealink says they managed to negotiate "fast track outcomes" which meant the ferry was released from dry dock on 18 May.

It then returned to Cape Jervis for final maintenance and the refitting of life rafts.

Sealink says it is adding extra journeys to its schedule and working to clear its waitlists as a priority.

Customers should keep checking the Sealink website for additional sailing times.