Lawsuits challenge DEQ approvals of Big Sky development projects

Court rulings and new lawsuits criticize the Montana Department of Environmental Quality's review of environmental impacts from the Quarry subdivision and Gallatin Canyon sewer project.

Feb. 3, 2026 at 9:23pm

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A Gallatin County District Court judge ruled that the Montana Department of Environmental Quality (DEQ) failed to adequately review the water quality impacts of the Quarry subdivision in Big Sky. The nonprofit Upper Missouri River Waterkeeper had filed a lawsuit against the DEQ, and the court ordered the agency to conduct a more thorough environmental review. Separately, the Waterkeeper has filed a new lawsuit against the DEQ, alleging the agency did not provide proper public notice or participation opportunities for a pipeline project as part of the Gallatin Canyon sewer system development.

Why it matters

These lawsuits highlight ongoing concerns about the environmental impacts of development in the Big Sky area, particularly on the Gallatin River. The rulings and new legal challenges suggest the DEQ may not be adequately reviewing the full scope of environmental risks from projects like the Quarry subdivision and the Gallatin Canyon sewer system.

The details

In the Quarry subdivision case, the court found the DEQ did not take a "hard look" at the water quality impacts of the project's septic systems. The judge ruled the approval violated the Montana Constitution by not properly determining the subdivision's effects on the health of the Gallatin River, including its role in algal blooms. For the Gallatin Canyon sewer project, the Waterkeeper alleges the DEQ approved a pipeline design change without providing public notice or an environmental review.

  • On December 29, 2023, a Gallatin County District Court judge issued a ruling against the DEQ's approval of the Quarry subdivision.
  • On December 17, 2023, the Upper Missouri River Waterkeeper filed a new lawsuit against the DEQ over the Gallatin Canyon sewer project.

The players

Upper Missouri River Waterkeeper

A nonprofit organization that has filed multiple lawsuits against the DEQ over development projects in the Big Sky area, citing concerns about environmental impacts.

Montana Department of Environmental Quality (DEQ)

The state agency responsible for reviewing and approving development projects in Montana, including in the Big Sky area.

Big Sky Rock, LLC

The developer of the Quarry subdivision project in Big Sky.

Gallatin Canyon Water and Sewer District

A local district partnering with the Big Sky County Water and Sewer District on the Gallatin Canyon sewer system development project.

Big Sky County Water and Sewer District

A local district partnering with the Gallatin Canyon Water and Sewer District on the Gallatin Canyon sewer system development project.

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What they’re saying

“The community of Big Sky, it needs clarity and frankly—there's a right way and a wrong way to do any type of development and to address the liability of wastewater, we need to be shooting for best available treatment and simply getting rid of the liability.”

— Guy Alsentzer, Executive Director, Upper Missouri River Waterkeeper

“Massive infrastructure projects being approved behind closed doors, without public participation, is antithetical to democracy. DEQ is stacking the deck by considering pieces of a regional wastewater system in isolation. The public deserves—and the Montana Constitution guarantees—a transparent decisionmaking process that reviews the whole picture.”

— Guy Alsentzer, Executive Director, Upper Missouri River Waterkeeper

“There has to be a process for resolving those questions before a project moves forward. We have been transparent with the community for years, and public involvement is critical—but working through technical engineering details early prevents wasted effort and unnecessary cost.”

— Al Malinoski, Board Member, Big Sky County Water and Sewer District

“It would have been fiscally reckless not to proceed the way we did, but it's also frustrating to see this portrayed as environmentally irresponsible—when the opposite is true. This project is about protecting the canyon. Suggesting otherwise was misleading and disappointing.”

— Brian Wheeler, Board Chair, Big Sky County Water and Sewer District

What’s next

It is unclear exactly what the court's ruling on the Quarry subdivision will mean for the project's timeline, as the approval remains in place and construction is ongoing. The DEQ may choose to appeal the court order. The new lawsuit over the Gallatin Canyon sewer project pipeline is also still pending.

The takeaway

These legal challenges underscore the ongoing tensions between development and environmental protection in the Big Sky area. They suggest the DEQ may need to take a more rigorous and transparent approach to reviewing the full scope of potential environmental impacts from major projects like the Quarry subdivision and Gallatin Canyon sewer system.