Unending challenge. At the Mississippi River bottleneck at Reads Landing, where the Chippewa Riyer empties tons of western Wisconsin silt into the Mississippi annually. Dredging is a perennial chore for the Army Corps, which manages inland waterways. The challenge here for the Army Corps giant dredge Goetz: Keeping the Mississippi navigation channel at nine feet so barges don’t scrape bottom and get hung up. Image: Melanie Peterson