GREENVILLE, Miss. — Another day, another sandbar to clear on the clogged Mississippi River.

It’s a routine that’s settled in as the drought in the nation’s central states leaves the river without the rainfall that is its lifeblood. The river is fed by the third-largest watershed in the world — a large chunk of the U.S. and part of Canada — and drought in that area means lower water along the river. That can put a major hurting on industries that use the river to ship hundreds of millions of tons of products, from grain to gasoline, every year.

One estimate put barge industry losses at $1 billion the last time the river was this low, in 1988. That’s why dredges, which knock down shallow spots and clear the shipping channel, are so vital in times like these. Shallow spots have already shut down the river at times this year, and the U.S. Army Corps of Engineers has asked to close it again for about 12 hours on Monday, this time for dredging near Baton Rouge, La.

Aboard the Dredge Jadwin, a massive-four story hulk that’s working around the clock to clear channels at Greenville, crews are pumping enough material from the river bottom every day to cover a football field 40 feet deep with sand and Mississippi mud.

Dredging is a way of life on the river because its upstream tributaries wash enormous amounts of silt each year down to the Gulf of Mexico.

But veterans like the Jadwin’s quality control officer, Bobby Justice, say they’ve never seen the river quite like this.

“This year we’re dredging in spots we usually don’t,” he said.

The dredge worked for just over a week to deepen the channel north of Greenville and widen it at one of the river’s many bends. It then moved a few miles downriver to another trouble spot where a barge ran aground this week, temporarily shutting down the river.