Mississippi River shipping interests are warning that commercial traffic will grind to a halt in December because of a combination of slower Missouri River inflows and obstructions, and they’re urging that Congress take action.

The requests come as the U.S. Army Corps of Engineers plans to gradually ease the flow of water out of its Gavins Point Dam in Yankton, S.D., a move aimed at preserving water levels in the drought-stricken reservoir system.

Those restrictions, however, will lead to navigation problems from Cairo, Ill., to St. Louis, shipping industry officials say. The Missouri is the main source of water on the Mississippi in that area, and restrictions combined with blockages in the area will mean big problems, they say.

The impact on the river in the Quad-Cities is likely to be minimal, said Jim Stiman, chief of water control for the Corps’ Rock Island district. The river is mostly shut down over the winter months because of ice, anyway.

The Illinois Waterway is open nearly year-round, however, and commodities flowing to and from Chicago will feel the pinch, said Larry Daily, president of Bettendorf-based Alter Logistics, which consults with shipping interests.

“That will be very heavily impacted,” he said.

As a result, consumers also could feel it, he said.

On Thursday, the American Waterways Operators and Waterways Council Inc. called on Congress and the Obama administration to get involved.

They warned that lower flows and rock formations in two places on the river south of St. Louis will bring traffic to a halt in the middle Mississippi about Dec. 10.

And they said lawmakers should clear hurdles so that work on removing the formations can be sped up to remove them.

At the same time, they also want Congress to consider “additional measures” to “preserve water levels that support navigation ...”

The groups represent barge operators, ports and agricultural groups, among others.

Curtailing the planned flow restrictions out of the Gavins Point Dam could be difficult. Last month, the Corps’ Northwest Division said runoff in October was below normal levels for the eighth consecutive month and that it needed to lower outflow as part of its drought conservation plan.

In the third week of November, the Corps plans to begin gradually reducing flow to 12,000 cubic feet per second. It’s normally at 17,000.

A Corps spokesperson said that in September, the reservoir experienced its lowest monthly inflow since 1898, when records were first kept, according to Reuters. The spokesperson said that inflows into the reservoir were 25 percent of normal.