A Federal Court judge has ruled against a contentious mine proposal in central British Columbia, upholding Ottawa's decision to reject the project over concerns it would adversely affect the environment.

A pair of decisions, released this week, mark the latest blow for Taseko Mines Ltd.'s New Prosperity mine, which is opposed by local First Nations, has been rejected twice by the federal government and has been the subject of years of litigation. The company says it's reviewing the court decision.

The New Prosperity project is a proposed open-pit copper and gold mine located 125 kilometres southwest of Williams Lake, B.C., near the Xeni Gwet'in First Nation community, part of the Tsilhqot'in Nation.

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While the project received the approval of the former B.C. Liberal government, the federal government under the Conservatives rejected it twice, most recently in 2014. Among the concerns was the impact on Fish Lake, which the Tsilhqot'in National Government considers a sacred site.

Taseko challenged that decision, as well as the findings of a federal environmental assessment report, but lost on both fronts. The Federal Court judgment concludes the process was fair.

Councillor Marilyn Baptiste, a former chief of the Xeni Gwet'in First Nations Government, said the decision was an important victory against the New Prosperity proposal.

"One of the biggest things that our elders would appreciate when they hear this is our voice is heard," she said. "That is one of the most important pieces to our elders and our people on the ground after decades of struggle to protect our area; it is vindicated, it is a great victory."

The proposal was named Prosperity before it went into its first environmental assessment process. In this proposal, Taseko said it would need to drain Fish Lake in order to build the mine, according to Sean Nixon, a lawyer with the environmental group Ecojustice who was involved with the first judicial review.

Fish Lake (Teztan Biny in Tsilhqot'in language) is located directly next to the proposed project. The Tilhqot'in National Government says the lake is also important in the nation's food fishery and is a cultural school. It is also adjacent to an area covered by a landmark 2014 Supreme Court of Canada ruling that awarded Tilhqot'in aboriginal title to 1,750 square kilometres of land in the B.C. Interior.

After the initial proposal was rejected by the federal government, Taseko changed the name of the project to New Prosperity and returned with a revised plan designed to save the lake, although a subsequent review found it would still be damaging.

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Brian Battison, vice-president of corporate affairs at Taseko, said the company is reviewing the decision but otherwise did not comment on the judgment or the impact on the project.

A B.C. Environment Ministry spokesperson said in an e-mail that the province is reviewing the decision. The federal Environment Minister wasn't available for comment.

Jamie Kneen, communication co-ordinator at MiningWatch Canada, said the group is pleased with the federal ruling.

"[The environmental assessment] did a decent job and came up with a sound recommendation. So, having that upheld by the federal court was heartening," he said.

According to a report by Taseko, the New Prosperity mining project would have had the potential to have significant economic and social effects, with annual production averaging 110 million pounds of copper and 234,000 ounces of gold over the mine life.

However, an environmental review panel concluded the New Prosperity project would seep more toxic water from the tailings storage facility than estimated. Additionally, concerns for the wildlife in the area owing to disruption of habitat were put forth.