It may be North America's largest waterway, but even the mighty Mississippi is being choked by drought, as historically low water levels threaten to halt the flow of vital commodities from the heart of the United States, with potentially devastating economic consequences.
Last year's northern summer saw the country's worst drought for more than 50 years, damaging crops across the Midwest and making stretches of the Mississippi perilously shallow and narrow for barge traffic, which carries about US$7 billion ($8.5 billion) of grain, coal, crude oil, cement and other commodities along the river in December and January.
Two trade groups, the American Waterways Operators and Waterways Council, warned last week that water levels had fallen faster than anticipated, and a section of the river might become impassable by Friday. The groups estimate a closure till the end of the month would affect about 8000 jobs, US$54 million in wages and benefits, and 7.2 million tonnes of commodities, worth US$2.8 billion.
Debra Colbert, senior vice-president of the Waterways Council, said: "We have never had an extended closure on the Mississippi. This is the height of the export shipping season. From now until March more than 60 per cent of the nation's grain moves on the inland waterway, bound for export. The impacts are going to be enormous, not only to barge and towing operators, but also to farmers, shippers and producers, and those who rely on the waterways."
Responsibility for keeping the shipping channel open falls to the Army Corps of Engineers, which said the drought-induced crisis was equal to or worse than any others in the past five decades. The corps has conducted regular dredging since July, and is now blasting hazardous underwater limestone formations to maintain a safe depth. It is also tackling an ice problem, as the river freezes over in shallow sections.
Last Thursday, the agency released extra water into the Mississippi from Carlyle Lake in southern Illinois.
The region's senators recently wrote to President Barack Obama, pressing for more water to be allowed into the Mississippi from the Missouri River, which it meets north of St Louis. The Corps of Engineers cut the flow of the Missouri by two-thirds in November to stock reservoirs, assuaging drought in more northerly states.
The worst-affected stretch runs from St Louis, Missouri, about 290km south to Cairo, Illinois, where the Mississippi is met by the Ohio River.
A depth gauge at Thebes measured just 1.8m last week. The National Weather Service forecasts a drop to 1m by Friday, and as low as 0.5m before the end of January. The minimum depth for the safe passage of most barges is 2.5m.