No. 52 and No. 53 have been waiting to be blown up since 1998, when a new mega-dam near Olmsted, Ill., was supposed to be finished. Authorized in 1988, the project is now wildly over budget and decades behind schedule. What was supposed to cost $775 million and be finished in 1998 will now most likely cost $2.9 billion and be operational in October 2018 at the earliest.

Image Luther Helland, lockmaster, looking out onto Lock and Dam No. 52 in September. Goods shipped by water from the Gulf of Mexico and the Mississippi River to points east pass through the dam, which was completed in 1929. Credit... Whitney Curtis for The New York Times

Gridlock at the Dam

Capt. David Stansbury was in the pilot house of the towboat William Hank, which was tied to a fleet of barges near Metropolis, Ill., waiting for its turn to pass through 52’s lock. “What would happen if both lanes of Interstate 95 were completely shut down for three or four days?” he asked. “You’re talking total gridlock in a major metropolitan area — this is the equivalent of that.”

Right now, the inland waterways are out of most Americans’ sights and minds. “If 52 does fail, or one of the other locks fails, and you cut off half the United States from their barge traffic, then you’ll see a public outcry,” Mr. Stansbury said. He explained: If corn cannot get to the factories, the price of any grain-based product will go up, and people will say, “What do you mean I’ve got to pay $10 for a box of cornflakes? Are you out of your mind?”

A towboat and its barges need at least nine feet of water to stay afloat. To guarantee this depth from, say, Pittsburgh to Cairo, Ill., a distance of 980 miles, the United States Army Corps of Engineers built dams. The dams make pools. Each pool is like a step, climbing from sea level to the Appalachians, say, or St. Paul. To get from one step to another, boats use water elevators, called locks, that raise anything that floats from one pool to another. Before the locks and dams, many rivers in the United States were low enough to walk across during dry months.

On an overcast September morning, the William Hank was pushing 13 barges — two tankers of soybean oil, one barge of dry cement, one barge of aluminum ingots, three barges of scrap steel, four barges of iron ingots, one barge of wheat and one of grain — a total of 19,200 tons of cargo, worth around $6.5 million. Most towboats push a 15-barge tow, which holds the equivalent of 225 train cars or 1,050 truckloads. There is a lot at stake when this much stuff is late.

In a low orange-trimmed building on the outskirts of Paducah, Ky., are the offices of Tennessee Valley Towing, which owns the William Hank. Gordon Southern, the company’s senior vice president, calculated that the 15-hour river closure on Sept. 14 cost him around $80,000. His company is just one of dozens.