The British Columbia government has issued an environmental assessment certificate for the contentious container port expansion project at Roberts Bank, despite acknowledging the project is likely environmentally harmful.

In a media release, the province said not granting the certificate would prevent B.C. from safeguarding provincial interests.

It noted that the project is almost entirely on federal land, within federal jurisdiction and already approved by Ottawa, and that "a decision not to issue a B.C. certificate could not prohibit the project from going forward."

"We understand the likely adverse environmental effects from RBT2 [Roberts Bank Terminal 2] and issue this certificate to provide provincial oversight, mitigation measures and requirements for the project to proceed," said provincial Environment Minister George Heyman and Transportation Minister Rob Fleming in a statement of reasons.

The project will greatly expand the existing container port at Roberts Bank in Delta, just south of Vancouver, by adding a large piece of land the artificial peninsula of the existing terminal, which sticks out into the Salish Sea.

The new terminal will house three additional freighter berths capable of handling another 2.4 million 20-foot shipping containers annually. Additionally, the Roberts Bank causeway will need to be widened to accommodate additional road and rail infrastructure.

Environmental groups that oppose the expansion said they were disappointed but not surprised.

Peter Ross, senior scientist with the Raincoast Conservation Foundation, said most concerning is that the expansion will further disturb one of the most diverse and productive areas of B.C., if not Canada.

"It signals yet again that another level of government is not out there to protect our natural resources, to protect southern resident killer whales that are deemed to be endangered under the Species at Risk Act," said Ross.

"[It's] another signal that salmon and fish habitat and Indigenous food security are secondary to very conservative-oriented economic projects."

The federal government approved the project back in April, imposing 370 conditions meant to address environmental concerns. The decision statement said RBT2 is likely to cause significant adverse environmental effects.

The B.C. certificate has 16 conditions, including a wetland management plan, a wildlife management plan and a greenhouse-gas reduction plan for emissions.

"We are of the view that it is important for us to ensure that we exercise our ability to add conditions that address provincial interests," said Heyman and Fleming. "We will continue to work with the federal government to ensure that strong protections within its jurisdiction are put in place and enforced."

Conservationists, labour unions and Indigenous nations on both sides of the Canada-U.S. border have all expressed strong opposition to the project.

The province said it is aware that two parties are asking for a judicial review of the federal decision to approve the expansion, but Heyman and Fleming decided to issue the certificate to make sure the project doesn't go forward without addressing their concerns.

The Vancouver Fraser Port Authority, which proposed the project, says the expansion is needed to prevent a capacity bottleneck at the Canada Pacific Gateway, the country's most important trade corridor with more than $275 billion in trade passing through each year.

The RBT2 construction is expected to cost $2 billion and will be payed for through private investment, fees and long-term leases of port facilities. It's estimated the terminal could take six years to build.