Federal officials hope a massive effort to remove silt and sand deposits from the bed of the Mississippi River in Minnesota will have cleared a path for hundreds of tied-up barges carrying millions of dollars in cargo to resume their trips downstream over the weekend.

Commercial barge traffic has been choked off for weeks by large sediment deposits in the Mississippi left behind by flooding from heavy spring and summer showers. Combined with a late thaw, it’s been “a perfect storm for the industry,” delaying shipments up and down one of the nation’s most important waterways, said Steve Tapp of U.S. Army Corps of Engineers, which is leading the cleanup.

The corps brought in four dredges to churn up enormous deposits near the southern Minnesota towns of Winona and Wabasha, suck them up and spit them onto boats to be carried to shore. With those areas clear, the four dredges and two additional crews will fan out to other sand-clogged stretches of the river to ease barges’ passage.

The delays have stretched dangerously close to grain harvesting season, when barges need to carry wheat, soybeans and corn from throughout the Midwest down to the Gulf Coast for export.

“We are looking at a very large grain crop. That has got people on pins and needles,” said Jerry Fruin, a retired economics professor from the University of Minnesota.

Dredging the Mississippi is part of regular river maintenance, but Tapp said this year’s work — and barge backup — is the worst in his 25 years of cleanups.

A brutally cold winter kept Lake Pepin — part of the Mississippi River — frozen into the start of this year’s shipping season, blocking traffic. Heavy rains in April, June and July raised the river too high for some locks, dams and the corps’ dredging equipment to operate. As they receded, the flood waters dropped shoals of sediment throughout the river.

“When the water dropped out, it dropped out fast. It left a lot of problems with us,” Tapp said.

The U.S. Coast Guard makes the final call on halting commercial traffic based on the corps’ recommendation. It closed the stretch of the river near Wabasha on July 19 and another near Winona — some 30 miles downstream — on July 23.

“We don’t believe traffic can pass through there until we dredge it,” Tapp said.

As of Tuesday, at least 350 barges were tied up throughout the region, waiting for clearance to move downstream, Tapp said. The sandbars have also blocked cement shipments from the south, though the corps has allowed several lighter-packed barges to travel upstream to feed construction season in Minneapolis and St. Paul, Tapp said.

The corps has sent out boats to find other potentially problematic areas along the river and will issue an emergency request on Wednesday to contract another dredging unit to assist the cleanup.

“We’re very aware of how serious it is,” Tapp said. “It’s going to be a mad push.”