CHICAGO - Flooding halted barge traffic on the Illinois River on Wednesday and high water levels prompted futures market operator CME Group Inc to declare force majeure for all corn and soybean shipping stations for the first time in more than two years. Barge lines have voluntarily stopped shipping traffic after heavy rains, river merchants said. CME, which owns the Chicago Board of Trade (CBOT) and other markets, said a majority of shipping stations on the river were unable to load crops due to high water levels. Traders said the disruptions would likely have a limited impact on grain trading because they will probably be over before the end of the month, when traders can begin delivering crops against futures contracts. The Illinois River is forecast to crest at many locations by early next week, according to the National Weather Service. Supplies of corn and soy, shipped by companies such as Cargill Inc, Archer Daniels Midland Co and Bunge Ltd, are large after U.S. massive harvests last year. Cargill, ADM and Bunge, which control the river, may advise CME at any time that loading conditions have improved, Rich Feltes, head of Market Insights for broker RJ O’Brien, said in a note. The shipping stations are delivery points for crops traded on the CBOT, and the declaration of force majeure allows a delay of contracted deliveries. Under exchange rules, if barges cannot be loaded at a majority of shipping stations, shipments may be delayed for the duration of the problem. Only 25 corn contracts, representing 125,000 bushels, were registered for delivery at the CBOT as of Tuesday, company data show. No soybean contracts were registered for delivery. In the cash market for grains, spot premiums for soybean barges delivered to Gulf Coast export terminals surged in response to the shipping disruptions. June-loaded soybean barges, including insurance and freight, traded as high as 102 cents over the CBOT July futures contract, up 12 cents from Tuesday and the highest spot basis since December, traders said. The basis reaction was more tempered in corn because the overall number of corn barges available in the river market is seasonally much greater, they said. Corn barges represented nearly 80 percent of total overall barge movements in the week ended June 6, the most recent USDA data showed. Only 19 percent were loaded with soybeans. If the halt in movement on the river drags on, elevators may need to suspend purchases of crops from farmers because they only have limited storage space, said Arlan Suderman, senior market analyst for Water Street Solutions.