A popular river that feeds the Boundary Waters Canoe Area Wilderness was named one of the most endangered rivers in the country Wednesday by a national conservation group that creates the annual list to draw public attention to environmental conflicts.

The South Kawishiwi — a clean, cold river near Ely, Minn., that tumbles out of the BWCA and then back into it — is threatened by copper mining projects pending along its banks and on the doorstep of the BWCA, American Rivers said in announcing the new list.

Twin Metals LLC, a joint venture partly owned by Duluth Metals Ltd. of Canada, has been conducting exploratory drilling on federal, state and private land in the area and plans to propose what could be one of the world's largest copper mines once it taps into an internationally significant body of ore that runs through northeastern Minnesota. A second project, PolyMet Mining Corp.'s open pit mine proposed for a site near Hoyt Lakes, drains into the St. Louis River and Lake Superior.

American Rivers said the BWCA and the Kawishiwi, sixth on the list of 10 rivers, "will be irreparably harmed" by acid mine drainage, which at other mines around the world has caused major environmental damage from sulfate and heavy metals that leach into local water.

The report, "America's Most Endangered Rivers," is "a call to action to save rivers that are facing a critical tipping point," said Jessie Thomas-Blate of American Rivers. "We hope citizens will take action to ensure a healthy Boundary Waters for generations to come."

Bob McFarlin, spokesman for Twin Metals, said the company plans to meet all state and federal environmental standards for the proposed mine, and that the project will undergo an extensive environmental review.

Minnesota environmental groups nominated the Kawishiwi for the endangered list. Test drilling sites were identified near Ely, Minn., in 2011.

"The bottom line is that the BWCA is going to be protected. The company is committed to it and state and federal law demands it," he said.

Twin Metals has said it is still assessing its construction but that it plans an underground mining project that would reduce the footprint of the project and environmental risks. Waste rock will be stored underground, minimizing exposure to the elements and the runoff that pollutes the water.

But environmental groups in Minnesota, including Friends of the Boundary Waters Wilderness, which nominated the Kawishiwi for the list, say the risks for the wilderness and Minnesota's northern lakes and rivers are enormous, and that all hard rock mines create environmental damage of some kind.

"The Boundary Waters is a unique and beloved wilderness of lakes of rivers," said Betsy Daub, the group's policy director. "The region should not be a guinea pig for risky new mines, which have never before operated without causing serious water pollution."

The Kawishiwi is a popular entry point to the BWCA and is a source of drinking water for Minnesota residents and visitors.

The mine, proposed within the Superior National Forest and just outside the wilderness area, would produce large quantities of waste rock, sulfuric acid and a variety of toxic metals, the group said. Polluted runoff from the mine poses a public health concern because of fish and drinking water contamination and threatens the BWCA ecosystem, it said.

McFarlin said that the project will be held to the highest environmental standards in the world. "And if the project doesn't pass that test, then it won't be allowed to proceed," he said.

The most endangered river on the American Rivers 2013 list is the Colorado River, which is threatened by outdated water management that allows for overuse, the group said. Others include the Little Plover in Wisconsin, which is also threatened from overuse of groundwater that feeds it; the Rough & Ready and Baldface Creeks in Oregon, which are threatened by nickel mining; and others in the Southeast and West that the group says are threatened by coal mining and coal ash deposits.

Minnesota's rivers have made the list before.

The St. Croix River has made it twice — once in 2009 because of sediment, fertilizers and other contaminants, primarily south of Stillwater, and again in 2011 because of federal legislation that would exempt it from long-standing federal protections as a wild and scenic river. Construction on the proposed four-lane bridge between Stillwater and Wisconsin is expected to begin this month. In 2011, the Cedar River in southeast Minnesota made the list because of "outdated flood management and poor watershed planning." The Minnesota and Mississippi rivers have also made the list in the past.

Josephine Marcotty • 612-673-7394