ST. LOUIS – 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 last week’s dayslong shutdown of the river’s busiest lock.

U.S. senators from Illinois, Missouri and Iowa this week 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., last week 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.