A simple mechanical fault has delayed the operation to move an orphaned killer whale from off the coast of Seattle in the United States to its family pod 740 kilometres (460 miles) away in Canada.

Officials have spent weeks struggling with medical and logistical issues but engine failure on the high-speed catamaran to be used for the operation provided the latest problem.

The orca, known as Springer, was due to have been hoisted onto the craft at dawn on Friday from its holding pen in Puget Sound but an engine on the catamaran became clogged and it had to return to port.

Springer has attracted international attention since being discovered swimming in the area in January in poor health.

Officials could not say on Friday if the next attempt to collect the orca would have to wait until the weekend.

Scientists plan to return Springer to her natural summer waters near Telegraph Cove in British Colombia in the hope that she will rejoin members of her family pod.

They are optimistic for the future of the young whale, who has regained her health after numerous early setbacks and now has a "passport" allowing her to travel.

Health problems

Scientists believe the 545-kilogramme (1,200 pound) whale became lost after being separated from her pod or was rejected after her mother died.

Known officially as A-73 for her place in her pod, she was suffering health problems including a skin rash, bad breath and worms that reduced her appetite.

Keiko was in captivity for 20 years

US officials - also worried that she could be hurt in the busy channel - agreed to capture Springer so she could be treated.

They declared her fit to travel and Canada gave her travel papers after deciding she would not be a hazard to other whales.

The catamaran journey to Telegraph Cove is due to take 10-12 hours.

Lance Barrett-Lennard, senior whale expert at the Vancouver Aquarium which is overseeing the transfer, said he was more hopeful of success with Springer than with Keiko - star of the "Free Willy" film - who has not yet returned to the wild.

But he said: "We will consider this a success if she lives her life out in the wild, even if she lived independently."