Environmental campaigners are suing the Trump administration for allegedly failing to protect the ocean habitat of a species of critically endangered killer whale.

The Centre for Biological Diversity has filed a lawsuit against the National Marine Fisheries Service, arguing it has left the last remaining southern resident killer whales at risk.

The population of the imperilled orca species off the US west coast is at its lowest in more than 30 years, numbering just 75.

The lawsuit was issued just days after a killer whale carried her dead calf for a record 17 days in a “tour of grief” before finally letting the body go.

Since the new millennium, the southern resident killer whale population, which forages and migrates off the coasts of Washington, Oregon and California, has suffered a high mortality rate.

Three in four newborns have not survived over the past two decades, and not one youngster born in the past three years has survived.

“Time is running out fast for these magnificent, intelligent orcas,” said Catherine Kilduff, a lawyer for the group.

“It’s heartbreaking to watch them starving to death and mourning their dead calves.

"Every day that Trump’s people delay action is a step toward extinction for these whales.”

Campaigners say the killer whales are starving because of a lack of fish, caused by the building of hydroelectric dams that have disrupted salmon populations in the region.

Water pollution from pesticides and other chemicals, noise and disruption by boat traffic and human encroachment in the Salish Sea – which stretches south of Seattle to north of Vancouver - have also disturbed and damaged orca populations and their habitats.

The Centre for Biological Diversity says the fisheries service failed to act on a 2014 petition calling for an expansion of protected habitats.

The fisheries service did agree that expanded habitat protections were needed but the Trump administration has failed to implement any, despite broad public support for them, say campaigners.

Southern resident killer whales represent the smallest of four resident communities in the north-eastern area of the Pacific Ocean. They travel extensively along the US west coast in winter and early spring, congregating near coastal rivers to rest and feed on migrating salmon.

They are the only killer whale population listed under the Endangered Species Act, which bans activities that will destroy or harm critical habitats.

“Federal law requires protection of endangered species’ habitat. Our basic humanity should lead us to help prevent these beloved orcas from dying out right in front of our eyes,” Ms Kilduff said.

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“So now we’re turning to the courts to compel the Trump administration to do the right thing.”