Total downbound barge traffic through the locking system of the Mississippi, Illinois, Ohio, and Arkansas rivers has decreased the last three weeks, the U.S. Department of Agriculture said today.

Water levels have rapidly declined since flooding and high-water events earlier this year. Lower water levels, aggravated by increased sediments deposited during the flood stages, have resulted in grounding hazards, with several barge groundings this month, the USDA said in its weekly Grain Transportation Report (GTR).

The Coast Guard and Army Corps of Engineers have issued warnings to mariners to reduce speeds and proceed with caution along portions of the inland waterways. Corps lock maintenance and dredging operations have also caused delays and traffic restrictions in some areas. These navigational issues, combined with recent high barge shipping rates and a low supply of barges upriver, have decreased the number of grain barges and volume of grain transiting the locks, according to the GTR. The number of barges unloaded at the Port of New Orleans has remained high, suggesting increased grain shipments are arriving from elevators south of the locking portion of the river system.

For the week ending Aug. 17, barge grain movements totaled 547,342 tons. This represents a 3.5% decrease from the previous week and 23% less than the same period last year, the USDA said. For the week ending Aug. 17, 348 grain barges moved down river. This is 20 fewer barges than the previous week. There were 682 grain barges unloaded in New Orleans, 3% less than the previous week, according to the USDA.