Four Minnesota Ojibwe tribes have appealed state utility regulators' approval of an environmental-impact statement for Enbridge's controversial new oil pipeline across northern Minnesota.

The tribes filed the challenge this week with the Minnesota Court of Appeals, saying the Minnesota Public Utilities Commission (PUC) erred by concluding that the environmental-impact statement adequately addressed negative impacts of the new pipeline.

Two other groups, Honor the Earth and Friends of the Headwaters, also this week filed appeals of the PUC's March approval of the environmental-impact statement. The environmental study, conducted by the Minnesota Department of Commerce, is required for Enbridge's $2.6 billion Line 3 project to move forward.

The PUC in June approved a "certificate of need" for the new pipeline, essentially a construction permit. That decision is also expected to be challenged before the Minnesota Court of Appeals. The PUC essentially agreed with Enbridge that the current Line 3, which is corroding and can only operate at half capacity, is a safety hazard.

The four tribes filing the appeal are the Fond du Lac Band of Lake Superior Chippewa, the Mille Lacs Band of Ojibwe, the Red Lake Band of Chippewa Indians and the White Earth Band of Ojibwe.

The Leech Lake tribe, another major Ojibwe band, is not part of the appeal. While the Leech Lake band has generally been against pipelines, it made clear during PUC hearings that it would rather see the construction of a new pipeline than the continued use of old Line 3.

Line 3, along with five other Enbridge pipelines, cross both the Leech Lake and Fond du Lac reservations on the way to Superior, Wis. As currently proposed, Enbridge's new Line 3 wouldn't cross any reservations, but it would traverse land where the tribes claim treaty rights to hunt, fish and gather.

Tribal and environmental groups fear Line 3's new route will expose a new region of wild-rice waters, rivers and streams to degradation from possible oil spills. The environmental-impact statement "fails to adequately address the impacts that the route will have both on environmental and tribal resources," the tribes' suit said.

When the PUC approved the new pipeline, it made one small alteration to Enbridge's proposed route, moving Line 3 farther away from Big Sandy Lake, which has particular cultural and historic significant to the Ojibwe.

The alteration will involve running a stretch of new pipeline closer to the Fond du Lac reservation, or possibly using the path of current Line 3 on the reservation — presenting the tribe with a dilemma.

The path through the reservation is the shortest route to avoid Big Sandy Lake.

The Fond du Lac band, in a PUC filing earlier this month, said it's "willing to consider an agreement with Enbridge" to allow the Big Sandy workaround to follow current Line 3's path.

The matter is currently in a "discussion" stage, according to the tribes' appeal.