(CBS News) MEMPHIS, Tenn. - Sweat beads on Chad Clark's bald head and runs down his flushed cheeks like rain drops on a windshield.
"Tight wire!" he yells at the rest of his barge crew, thick fingers yanking even thicker levers with all his might. They are trying to make sure the barge stays together in the extremely low water.
Clark is first mate on a tow pushing a massive barge down the mighty Mississippi. The perfect piles of coal in deep red containers, like rows of black macaroons on a baking sheet, are his responsibility.
"It can be dangerous," he says, looking out over his cargo with pride of someone who grew up on this river. "Anything could happen. There could be groundings."
Clark and his crew are making sure the cables holding the giant barge together are as tight as possible because a mild winter and the drought have the Mississippi way below its normal levels. Today it's 10 feet down and we float past sandy beaches as if we are in the outer banks of North Carolina.
"I've never seen it this low," he says. To make it down the river, they have to carry 20 percent less of what they normally would.
"At this point, it's so low that if it were heavier you would scrape the bottom?" I ask.
"Yes ma'am, that is correct."
There have already been multiple groundings. Three steep floors up in the stately wheel house, Capt. Roy Daniels has his eyes fixed on the water. Islands the size of a strip mall have sprung up on the Arkansas side of the river. We are approaching one of the two bridges he must pass under through Memphis and the channel in which to do that is now like a single lane country road.
"I want to make sure to be right," he says in a soft Southern twang not taking his eyes off the river, "so we don't have an incident or run aground or knock a barge out of tow."
To steer, he lightly pulls on two shiny levers on each side of him and closely watches the high-tech depth scanners on his control panel. It's literally like threading a needle -- the channel is now so thin and everyone seems to hold their breath as we glide between the massive oblong pillars.
He picks up the black phone next to his knee. "This is Capt. Roy Daniels, we've cleared the bridge."
He lets out his breath and a smile seeps across his face.
"You just have to pay attention, make sure you watch everything," he says with a Southerner's gift for understatement.
It's a lot lower than it normally is. It's always changing. A year ago, it was flooding. Last year's flood markings on the rocky banks along our left are literally five stories up from where we are on the water.
"You have to have less cargo on your barge and you have to go slower?" I ask.
"That's right," he says staring out over the coal.
"And what is that doing to your business?"
"Pushing less cargo you know that is hurting them financially but at least we're still moving."
The river is a superhighway for the nation's commodities. Barges transport 60 percent of U.S. corn for export, 45 percent of soybeans, 22 percent of gas, and 20 percent of coal. And one barge can move as much as 70 trucks.
"Everything depends on the river being open," says Derrick Smith, an amiable 22-year veteran with the U.S. Army Corps of Engineers. We are on a tug boat getting a closer look the exposed weirs that the Corps has built since the record lows of 1988. They've put in hundreds of these stone dikes to direct the water into a channel that must be 9-feet deep and 300-feet wide on the lower Mississippi.
As the captain cuts the engine, you can hear the water churning, as if the river knows where it needs to go.
"What is the difference in the amount of traffic that can go down this river?" I ask.
"In high stages tow boats are like on a freeway all by themselves," said Smith. "They can maneuver anywhere you want. Today, towboats are basically on a one-way street. Have to pull over and wait for oncoming traffic, wait, slow down."
"Can you keep this river open?" I ask. His kind face hardens with determination.
"Absolutely. We have dredges and we'll go out and dredge the low areas. $160 billion of cargo a year moves up and down this system. You have to keep it going. We do. We have to keep it going."
Some barges have run aground and forecasters expect it to get worse as the drought is forecast to persist into the fall.
"If it keeps dropping, what are we looking at?" I ask.
"Possible river closures, traffic stopping while we dredge," Smith says.
"Could be devastating. Every family would see it. You'd see it at the gas pumps, you'd see it at the grocery stores. You'd see it everywhere."
"Tight wire!" Clark yells again the sweat dripping onto the cable.
"What do you hope for?" I ask him.
He puts his tanned hands on the hips of his oil stained paints. "I hope we get some water soon," he tips his chin with a weary smile. "Some snow this winter some rain."
Behind him we drift past a sandy beach as big as a grocery store parking lot. Just six weeks ago, it was completely underwater.