ST. LOUIS (AP) The Mississippi River’s 70-year-old system of locks and dams urgently needs upgrades to accommodate barges that have gotten bigger over time, a group of federal lawmakers is warning after a dayslong shutdown of the river’s busiest lock.

U.S. senators from Illinois, Missouri and Iowa sent a letter to the Environmental and Public Works Committee saying the locks and dams suffer from “a troubling lack of upkeep.”

Workers closed a lock just north of St. Louis near Granite City, Ill., to make emergency repairs to a towering metal cylinder that helps guide barges. A protection cell — a rock-filled steel cylinder against which barges rub to help align them for proper entry into the lock — had split open, spilling enough of the rock into the channel to obstruct passage.

Officials said that damage had less to do with the protection cell’s age than with the fact that an unarmored section that is normally submerged was exposed because the river’s level has been lowered dramatically amid one of the worst U.S. droughts in decades.

The lawmakers imploring for the system’s broader upgrades pointed out that those temporary repairs idled hundreds of barges, stalling shipments of everything from grains to coal, fertilizer and construction materials that typically make their way to points north and south — and often overseas.

“Unfortunately, a troubling lack of upkeep within this system has crippled our ability to move goods in a safe and efficient manner,” Sens. Dick Durbin and Mark Kirk of Illinois, Missouri’s Claire McCaskill and Roy Blunt, and Iowa’s Tom Harkin and Chuck Grassley wrote in their letter to the committee, which is considering a new water-projects bill.

“Continued shutdowns will impact the not just current shipments on the river but the overall reliability and timeliness of using the inland waterways system,” the senators added.

Roughly half of the nation’s farm exports pass through that Granite City lock. The shutdown came at a particularly bad time as growers throughout the Midwest are ramping up their harvests of corn before turning their attention to bringing in their soybeans.

Coast Guard and Army Corps of Engineers officials estimated that the closure of the lock, through which 73 million tons of cargo typically passes each year, stood to cost the shipping industry $2 million to $3 million a day in lost revenue.

The senators noted that the Mississippi is the backbone of the nation’s waterway transportation system, accounting for $12 billion worth of products shipped each year, including more than a billion bushels of grain to ports around the world.

“This efficient river transportation is of utmost importance to the nation,” they wrote. “Addressing the infrastructure needs of our inland waterways system is of significant national interest.”

The senators said the river’s locks-and-dam network is “in desperate need of modernization,” with many of the older locks stretching 600 ft. (183 m) in length, only half the expanse of most current barge tows.

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