The Daily Yonder This story was published in partnership with Grist. In 2009, App Thacker was hired to run a dredge along the Emory River in eastern Tennessee. Picture an industrialized fleet modeled after Huck Finn’s raft: Nicknamed Adelyn, Kylee, and Shirley, the blue, flat-bottomed boats used mechanical arms called cutterheads to dig up riverbeds and siphon the excavated sediment into shoreline canals. The largest dredge, a two-story behemoth called the Sandpiper, had pipes wide enough to swallow a push lawnmower. Smaller dredges like Thacker’s scuttled behind it, scooping up excess muck like fish skimming a whale’s corpse. They all had the same directive: Remove the thick grey sludge that clogged the Emory.