MINNEAPOLIS — The Minnesota Court of Appeals ruled Monday that AT&T Mobility LLC can build a 450-foot cellphone tower with flashing lights that would be visible within parts of the Boundary Waters Canoe Area Wilderness, overturning a lower court’s finding that the environmental impact of the tower would be detrimental.

The Friends of the Boundary Waters Wilderness had sued to block the 450-foot tower, saying its location atop a 150-foot-high ridge about 7.5 miles east of Ely and 1.5 miles outside the BWCAW would make it visible from 10 lakes within the protected area. The group argued that a 199-foot tower without lights would provide sufficient coverage to residents along the Fernberg Road corridor east of Ely, as well as expanded emergency service for paddlers within the wilderness area.

A three-judge panel wrote that a lower court erred by concluding that allowing the tower would have a “materially adverse effect on the environment.”

They said that the trial court failed to show that the negative effects of the proposed tower on the views within the Boundary Waters would be severe enough to justify blocking it.

AT&T said it now plans to replace the smaller tower, which recently became operational, with the taller tower without interrupting service.

“We agree with the Court of Appeals that the larger tower would not have a material adverse effect on the Boundary Waters,” spokesman Marty Richter said in an email. “On the contrary, we believe the limited impact of the tower is greatly outweighed by the benefits — including health and safety benefits — of the improved service it will provide residents and visitors. “

Paul Danicic, executive director of the Friends, said the ruling “seriously compromises” Minnesota’s ability to protect its scenic vistas. He said his group will review the ruling before deciding on further appeals. He also said AT&T has “perfectly viable” alternatives that would not impair America’s most-visited federally designated wilderness area.

“Thousands of our members firmly believe a 450-foot tower with a flashing red light on top that would be visible from several lakes up to 10 miles away would indeed harm the wilderness experience,” Danicic said.

The BWCA covers more than 1 million acres in northeastern Minnesota with more than 1,000 lakes and hundreds of miles of streams and rivers. Cellphone coverage is spotty in areas around Ely, one of the main gateways to the wilderness, and a few other areas close to civilization but it’s mostly unavailable elsewhere in the wilderness. The U.S. Forest Service warns visitors not to rely on getting a signal there.

Hennepin County District Judge Philip Bush ruled against the tall tower last August. But the Court of Appeals said he misapplied the Minnesota Environmental Rights Act, which allows citizens and groups to sue to protect the state’s natural resources, and a 1997 Minnesota Supreme Court ruling that laid out five factors for interpreting MERA, including “the quality and severity of any adverse effects” from a proposed project.

“The district court’s findings establish that less than 50 percent of the proposed tower will be visible from less than one percent of the BWCAW’s 1,175 lakes, several of which have scenic views that include signs of human existence. And the district court made no findings as to what degree of visibility from the less-than 1 percent of the lakes reaches the ‘severe’ threshold,” the appeals court ruled.

Another factor under the 1997 precedent is whether a proposal would have “significant consequential effects on other natural resources.” The appeals court said the district court’s findings that there would be negative effects on migratory birds wasn’t sufficient, noting that the judge concluded it was difficult to determine how many birds would be killed by the tower or how significant that effect would be.

“The district court’s failure to consider the possibility that the proposed tower may make the BWCAW accessible to more visitors is also of concern,” the appeals court said.

While the appeals court found merit to the judge’s conclusion that “the scenic views from the BWCAW where there are no permanent signs of man or modernity are rare and unique,” it also said the lower court’s findings as a whole weren’t sufficient to block the tower.