Lock repair to close part of Illinois River at least a week: Army Corps CHICAGO (Reuters) - Barge shipping returned to normal this week on most of the Illinois River after spring floods, but lock repairs will halt navigation on a northern stretch for at least a week beginning on Friday, the Army Corps of Engineers and Coast Guard said. Marseilles Lock and Dam near Seneca, Illinois, was critically damaged when seven barges broke loose from a tow on April 18, tearing 20-foot (6-meter) holes in two of the dam's gates. The Army Corps plans to draw down the pool of water above the lock by four feet so crews can construct a rock dike below the dam, the first step in a repair process that could take months to complete. "The river will be way below the nine-foot navigation requirement once we start the drawdown," said Allen Marshall, spokesman for the Army Corps Rock Island district, referring to the minimum depth most commercial boats need. "Right now the Coast Guard is coordinating getting barges and recreational boats out of the area," he said. The rock dike, expected to be completed by May 20, is aimed at reducing the flow of water through the damaged gates during repairs and may also help hold water in the Marseilles pool. The pool refers to the 27-mile (43-km) section of the river between the damaged lock and the next lock upriver, Dresden Island near Morris, Illinois. The rest of the repair project could take several months, although the Corps had no exact estimate yet. The area should reopen to navigation, possibly with some restrictions, as long as the dam can maintain a deep enough upriver pool. Grain shippers and barge operators have been scrambling this week to move vessels upriver or downriver from the lock and out of the Marseilles pool. "They told the industry that, basically, nobody will be able to go in and out of that pool with any loads so the river will effectively only be open from Marseilles south all next week," a barge broker said. "There's probably some people that won't get everything moved south of there but the majority will," he said. The Illinois River bisects the country's No. 2 corn- and soybean-producing state from Chicago to its confluence with the Mississippi River near Alton, Illinois. Both rivers are critical shipping arteries linking grain producers in the Midwest with export terminals at the Gulf, the exit point for about 60 percent of all U.S. grain exports. There are only five grain elevators upriver from Marseilles, one each in Seneca and Morris and the rest in Chicago, so the impact on grain shipments was minimal, traders said. Receding floodwaters on the rest of the river prompted the CME Group to lift its force majeure declaration on Illinois River cargoes. Reporting by Karl Plume; Editing by Dale Hudson