(Bloomberg) -- A crack in a bridge over the Mississippi River has stranded more than 700 barges, cutting off the biggest route for U.S. agricultural exports when the critical waterway is at its busiest.The route is shut near Memphis while the Tennessee Department of Transportation inspects a large crack in a highway bridge spanning the river, according to the U.S. Coast Guard. A queue has expanded to 47 vessels and 771 barges, with 430 of those heading north and the rest going south, Petty Officer Carlos Galarza of the Coast Guard’s 8th District said Thursday afternoon by email.The Mississippi River is the main artery for U.S. crop exports, with covered barges full of grain and soy floating to terminals along the Gulf of Mexico, while crude oil as well as imported steel also travel through sections of the waterway. Any sustained outage would disrupt shipments out of the Gulf. Corn futures tumbled by the most allowed under CME Group rules partly on speculation that exports would back up.“The river is the jugular for the export market in the Midwest for both corn and beans,” said Colin Hulse, a senior risk management consultant at StoneX in Kansas City. “The length of the blockage is important. If they cannot quickly get movement, then it is a big deal. If it slows or restricts movement for a longer period it can be a big deal as well.”The stoppage along the Mississippi River is the latest calamity to upend the commodities world in recent weeks. Back in March, the Suez Canal was blocked by a giant container ship that got stuck sideways in the vital waterway for almost a week, paralyzing global shipping. And late last week, a cyberattack brought down the largest fuel pipeline in the U.S. for five days, leading to widespread gasoline shortages from Florida to Virginia.A lengthy halt on the Mississippi River could further roil crop markets, where soybeans and corn futures have hit multiyear highs amid adverse weather in Latin America and a buying spree from China. Corn futures fell Thursday by the exchange limit of 40 cents, or 5.6%, to $6.7475 a bushel in Chicago.As a workaround, traders could in theory also send some supplies on trains and divert to ports along the U.S. Pacific Northwest. Few grain and soy buyers were bidding for barges north of the river closure amid uncertainty on when vessel traffic would resume.The crack halting vehicle and waterway traffic is in the truss of the Interstate 40 Hernando DeSoto Bridge, which was found during a routine inspection, according to a Tuesday statement from the Tennessee Department of Transportation.“The timeline is still undetermined” for the waterway reopening, department spokeswoman Nichole Lawrence said Thursday morning by email.The Army Corp of Engineers could figure out a way to keep automotive traffic closed in order for water traffic to resume under the bridge, according to CRU Group analyst Josh Spoores. It may cause bottlenecks, but most consumers already used to waiting months for supplies to ship are probably fine with some added delays, he said.The New Orleans Port Region moved 47% of waterborne agricultural exports in 2017, according to the U.S. Department of Agriculture. The majority of these exports were bulk grains and bulk grain products, such as corn, soybeans, animal feed and rice. The region also supports a significant amount of edible oil exports, such as soybean and corn oils and even attracted 13% of U.S. waterborne frozen poultry exports in 2017.Some traders speculated that, based on past experience, the river might be partially opened for restricted movements while repairs are being done.“My sense is that it is not a big deal for river traffic as it will be a short-term disruption,” said Stephen Nicholson, a senior analyst for grains and oilseeds at Rabobank. “The good news is most of fertilizer has already come up river and soybean exports are at their low point. However, corn exports continue at a strong pace, so we may see a slight delay in corn barges reaching” New Orleans.It may be difficult for exporters to shift much volume to rail, as the capacity to unload trains outside of the New Orleans area is limited, according to Curt Strubhar, vice chairman and risk management consultant at Advance Trading Inc.“There aren’t many rail unloaders South of the issue,” he said, adding that New Orleans “port elevators aren’t equipped to handle a sharply higher share of rail unloads either.”Of agricultural supplies that floated on barges north of Memphis, about 84% was corn and about 13% was soybeans, according to Mike Steenhoek, executive director of the Soy Transportation Coalition, citing USDA data. Overall shipments of corn and soy during the week ended May 8 were 18% higher than a year ago.Agricultural co-operative Growmark’s St. Louis port, which sends corn and soybeans south to New Orleans for export mostly to China and receives fertilizers, will likely close Friday, according to Matt Lurkins, executive director of the firm’s grain division.“Freight was already tight,” Lurkins said in a phone interview. “Then this kind of sent us over the edge.”If the pause drags on, he said, Growmark could send more grain to processors rather than loading it on barges for export.Small volumes of crude and partly refined oil are shipped by barge on the river as well. In February, 2.85 million barrels moved from the Midwest to the Gulf Coast via barge and tanker, according to government data.Imported steel on barges will be delayed as long as traffic is halted. About 25% of imported steel travels through at least a section of the Mississippi River, according to Wood Mackenzie analyst Cicero Machado, though he said newly arriving foreign steel to ports in New Orleans or Mobile, Alabama can be diverted onto rail cars or trucks.The river also is a major artery for steel shipments within the U.S. and delays could become an issue for automakers in the South that depend on high-strength steels produced in the Midwest, he said.“At this stage the big question is: is this going to last?” Machado said. “The issue is not actually in the river, it’s in a bridge over the river -- so perhaps they’re going to find a way to manage the traffic there.”(Adds Coast Guard update in second paragraph.)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.