Shippers and lawmakers are pressuring President Barack Obama to declare a federal emergency along the Mississippi River, citing potential “catastrophic consequences” in the Midwest if barge traffic is curtailed by low water on the nation’s busiest waterway.

They want the U.S. Army Corps of Engineers to hasten the planned removal of submerged rocks near Cairo, Illinois, that may impede barge traffic at low water levels.

They also want the Corps to stop its seasonal restriction on the flow of Missouri River water into the Mississippi, which it began last week, as there is still a lot of stuff to transport down the river before winter.

Mississippi River barge traffic is slowing as the worst drought in five decades combines with a seasonal dry period to push water levels to a near-record low.

Barges on the Mississippi handle about 60 percent of the nation’s grain exports entering the Gulf of Mexico through New Orleans, as well as 22 percent of its petroleum and 20 percent of its coal.