Shipping industry officials issued a new study Friday saying nearly 20,000 jobs are at risk if something isn’t done to prevent barge traffic from grinding to a halt along the Mississippi River in December.

Meanwhile, a group of lawmakers have joined the private sector in asking the Obama administration to take action.

The study, which was issued by the American Waterways Operators and Waterways Council Inc., says 4,100 barge jobs will be directly affected by the shutdown, and another 15,600 indirect positions also are at risk.

Industry officials say barge traffic will be stopped about Dec. 10 if the U.S. Army Corps of Engineers continues to restrict the flow of the Missouri River into the Mississippi and rock pinnacles south of St. Louis aren’t removed.

The drought has lowered water levels, exposing the pinnacles. Also, the Corps has begun limiting outflows from the Gavin’s Point Dam in Yankton, S.D. The Missouri is a major feeder into the Mississippi River near St. Louis.

If a portion of the Mississippi River is shut down, barge and port operators say, the impact will ripple throughout the Midwest economy.

The study said most of the jobs at risk are in Illinois, Louisiana and Missouri. Almost 1,500 barge jobs in Illinois would be affected. In Iowa, the number would be much less, 147. Indirect jobs at risk number 5,187 and 315, respectively.

“This is further evidence that there is a regional economic crisis in the making that necessitates action from the president, and these figures only take into account the months of December and January,” said Tom Allegretti, the president and chief executive of American Waterways.

It’s not clear how long it would take before barge operators would be laid off. Larry Daily, the president of Bettendorf-based Alter Logistics, said when his firm operated a fleet, it would idle workers during the winter months but continue to pay some benefits with the understanding the workers would return when business picked up. He said operators will want to keep the workers and their unique stills. But he said the duration of the shutdown will have an effect on that.

“They will do what they can to keep these people, but you can only do it so long before you’re laying the owner off,” Daily said Friday.

The nearly 20,000 jobs represent $130 million in wages and benefits, the study said.

The Corps is restricting flow out of the Gavin’s Point Dam because of record drought, officials say, and its master plan doesn’t allow it to alter the restrictions, which began about a week ago. That’s why industry officials are asking for a presidential declaration.

U.S. Sen. Tom Harkin, D-Iowa, said Friday a group of senators have joined the request for a presidential declaration. Several lawmakers met with the top Army official overseeing the Corps on Thursday and left saying they were encouraged. Industry officials, however, are worried it will take too long to take bids, award a contract and get to work on the pinnacles.

The Obama administration says it is studying all options.