Protesters — or water protectors, as they identify themselves — walk along Highway 1806, past a sprawling encampment at Standing Rock on Thursday. Thousands of people gathered to join the Standing Rock Sioux Tribe's protest of the Dakota Access Pipeline. Jessica Rinaldi/Boston Globe via Getty Images hide caption

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Jessica Rinaldi/Boston Globe via Getty Images

A member of the Stutsman County SWAT team who declined to give his name nor to be identifiable by badge stands guard by an armored personnel carrier equipped with an LRAD, or long range acoustic device, while deployed to watch protesters demonstrating against the Dakota Access Pipeline. John L. Mone/AP hide caption

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John L. Mone/AP

A view of the main trench to the permanent camp at Camp Century, Greenland, in the 1950s. The U.S. Army base was abandoned in 1967, after Greenland's ice sheet began shifting and the Army realized that the tunnels wouldn't last. Pictorial Parade/Archive Photos/Getty Images hide caption

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Pictorial Parade/Archive Photos/Getty Images

Melting Ice In Greenland Could Expose Serious Pollutants From Buried Army Base

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Water spills into New Orleans' Lower Ninth Ward through a failed floodwall along the Industrial Canal on Aug. 30, 2005, a day after Hurricane Katrina tore through the city Pool/AFP/Getty Images hide caption

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Billions Spent On Flood Barriers, But New Orleans Still A 'Fishbowl'

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A truck drives on top of a levee that protects a soybean field in New Madrid County, Mo., when the Mississippi River floods. Kristofor Husted/KBIA hide caption

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Kristofor Husted/KBIA

Army Corps Project Pits Farmland Against Flood Threat

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Roy Presson (C) embraced his daughters Catherine (L) and Amanda on Tuesday as they stood on the edge of State Highway HH looking out at their family farm in Wyatt, Mo. The Presson home and 2,400 acres of land that they farmed was flooded when the Army Corps of Engineers blew a massive hole in a levee at the confluence of the Mississippi and Ohio Rivers to help save the town of Cairo, Ill. Scott Olson/Getty Images hide caption

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Scott Olson/Getty Images