By the BBC's Janet Williams in Seattle

Scientists and environmental groups are growing increasingly concerned about the health of an orphaned baby orca whale off the north-west US coast.

The whale is living alone in the waters of Puget Sound off the city of Seattle. It is rare for orcas, also known as killer whales, to live by themselves.

The whale, first spotted in January, is malnourished and has parasites and skin infections.

The plight of the baby orca has started a heated debate about what should be done, if anything, to save her.

Malnourished

Workers on the local ferries have nicknamed the lonely whale Boo, the initials standing for Baby Orphaned Orca.

Scientists however know her as A73, a member of a whale pod living more than 400 kilometres (250 miles) to the north. Her mother is dead and the pod rejected her efforts to reunite with them.

Boo, who is less than two years old, arrived in the busy waters off Seattle in January.

Although she has been filmed eating fish, scientists say her weight is dropping, reducing her ability to fight off infections.

Aquarium

The marine authorities are in talks with conservationists about what should be done. The favoured option is to bring Boo into a pen still within Puget Sound and nurse her back to health.

The scientists warn, however, that there is little chance she will ever be accepted by her home pod - they are close communities which rarely take in outsiders.

The alternative is to take Boo into an aquarium. It is a sensitive subject here because in the 1970s almost half the local orcas were captured and turned into performance animals.

In recent years the number of whales has declined again as a result of increased shipping traffic, depleted fish stocks and continued pollution from toxins such as PCBs.