The WA Government has announced it will appeal against a Supreme Court decision which ruled environmental approvals for the controversial Roe 8 project were invalid.

Key points: WA Government to appeal against Supreme Court ruling that found environmental approvals for Roe 8 were invalid

WA Government to appeal against Supreme Court ruling that found environmental approvals for Roe 8 were invalid Roe 8 an essential piece of infrastructure that the Government remains committed to, Premier says

Roe 8 an essential piece of infrastructure that the Government remains committed to, Premier says New environmental approvals process to take up to a year

The Save Beeliar Wetlands group had brought the case to court, arguing the Environmental Protection Authority (EPA) did not take its own policies concerning land offsets into account when it assessed the project.

Their legal bid succeeded when, in December last year, Chief Justice Wayne Martin ruled the EPA's assessment and recommendation to Environment Minister Albert Jacob was invalid, along with his subsequent approval.

It prompted the Environment Minister to order an external review of the EPA, although he maintains the authority still has his full confidence.

Roe 8 is a key part of the $1.6 billion Perth Freight Link project, which seeks to build a by-way for heavy haulage from Perth's eastern industrial suburbs to Fremantle Port.

Thousands have attended rallies in protest against the project and drilling was disrupted by demonstrators when it began last month over fears it would destroy parts of the Beeliar Wetlands in Perth's south.

Premier Colin Barnett said the Government would ask the EPA to reassess Roe 8 and would also appeal against the Supreme Court's decision.

He said Roe 8 was essential infrastructure and the Government remained committed to its construction.

"It's important for the transport industry, particularly heavy vehicles," he said.

"It's important for the long-term viability of our ports, in terms of our role as a major exporter and also in terms of imports.

"It's also important in terms of reducing congestion and improving road safety in the southern suburbs.

"And it's also important for jobs. Roe 8 would have generated 2,500 direct jobs, plus many more indirect jobs."

Mr Barnett conceded the decision to appeal against the Supreme Court's ruling was a significant step to take.

"The decision of the Supreme Court ... related to the way in which policy guidelines of the EPA were used. That's quite a legal and technical issue," he said.

"While we acknowledge and respect the decision of the Supreme Court, the Government needs to respond. We have no option."

Roe 8 a Government failure: WA Labor

The Premier said the new approvals process for Roe 8 could take up to a year.

"We do hope it can be done in quicker time but that will be up to the EPA and the level of detail involved," he said.

"[It] may come down with the same result. It may add further conditions. We don't know.

"There will be full opportunity for public submissions and participation. Just like the original assessment."

Opposition transport spokeswoman Rita Saffioti said the State Government had an "unhealthy obsession" with the Roe 8 project.

She said the Supreme Court decision should have prompted the Government to consult with the community and make changes to its proposal, rather than fight to defend it.

"It is all over the place," Ms Saffioti said.

"They're appealing a decision that they're actually implementing and at the same time they're asking the EPA to review itself in relation to this decision.

"There was an opportunity for the Government to sit down and develop a better plan. They've failed.

"What we're seeing is more chaos and dysfunction from this Government."