But McCaskill said in a statement that action is needed immediately.
"This issue is impacting jobs and businesses in Missouri as we speak, so we don't have weeks to wait for a response from the Army Corps," McCaskill said. "It's time for the president to take action to protect our jobs and businesses."
At issue is the area of the Mississippi River between where the Missouri and Ohio rivers merge into it — roughly the 180 miles between St. Louis and Cairo, Ill. Barge navigation on the middle Mississippi becomes particularly tricky if the channel dips to around 9 feet of depth. Currently it is about 13 feet deep and National Weather Service hydrologists predict it will drop to around the 9-foot mark by around Dec. 10.
The corps has spent months dredging the river to try and keep the channel open. It plans to use explosives to remove rock formations near Thebes, Ill., and Grand Tower, Ill., that can endanger barges in low-water periods. But the bidding process is complicated and the work isn't expected to begin until early February.
The disaster declaration sought by the senators seeks to cut through red tape to expedite that removal. It would also seek to restore the Missouri River flow to around the normal level.
Goods such as grain, corn, coal, petroleum and chemicals are typically shipped along the Mississippi River, in part because the volume is so high that using trucks or trains would be far more costly. Waterway trade groups say that if the river was shut down starting next month and through January, the impact would reach into the billions of dollars.
AP reporter Jim Suhr in St. Louis contributed to this report.