Rick Calhoun says the drought that halted barge traffic on the Mississippi River last year would look like a comparatively minor problem if one of the nation’s aging locks and dams were to fail.

The lock and dam system, mostly built in the 1930s, has long outlived its life expectancy, according to the Cargill executive, and requires new investment by the federal government.

“It’s our fear that at some point in time we could have a failure, and actually shut down a lock or a dam for an extended period of time, doing severe economic harm,” said Calhoun, marine and terminal division president for Cargill, the Minnetonka-based agribusiness giant.

He has been speaking publicly on the state of the nation’s waterways in recent weeks, including at a U.S. Department of Agriculture conference in Washington last week.

Snowstorms have strafed the Midwest and river levels have risen in recent weeks, easing concerns that the 2013 shipping season will be a repeat of last year’s, with low river levels interfering with shipping on the Mississippi. But worries over the condition of the lock and dam system are lingering, with no end in sight.

“The infrastructure is in dire straits,” said Lee Nelson, president of Upper River Services Inc. in St. Paul, which moves barges between terminals on the river.

A 280-foot section of wall at the Lockport Canal near Chicago collapsed and slid into the Illinois Waterway in 2011.

In 2009, a lock gate fell off its hinges in Ohio and took five months to repair. Fortunately for Ohio River shippers, that lock had an auxiliary chamber to allow barge traffic to continue during repairs. But on the Upper Mississippi, “less than a handful” of the 27 locks have auxiliary chambers.

“If a similar situation were to happen at the majority of the locks on the Upper Mississippi, there is no auxiliary,” Nelson said. “If we have a lock fail, I’m done.”

About 60 percent of U.S. grain exports travel down the Mississippi to terminals in Louisiana, where corn and soybeans are loaded onto ships headed for foreign markets. Goods such as coal, cement and road ice come north to Minnesota by barge.

The Upper Mississippi from St. Louis north is regulated by locks and dams that limit the impact of drought but also must be maintained by the U.S. Army Corps of Engineers. The bulk of them were built to last only into the 1980s and 1990s.

“The Corps has done an admirable job of keeping them functioning,” Calhoun said.

The Corps this winter has been working on Lock and Dam No. 6 at Trempealeau, Wis. In a process called dewatering, engineers drain the lock, repair parts and patch concrete.

Patrick Moes, a spokesman for the Corps in St. Paul, said it’s true that the system is outdated, and that there are no plans for wholesale rebuilding in the foreseeable future.

“It’s not going to fall apart tomorrow, but we are aware that it’s outlived its life expectancy,” Moes said. “Maintenance only goes so far. We’re still trying to manage it and maintain it.”

Calhoun says there’s no reason to think any of the locks and dams will be rebuilt in the next 20 years. He said the federal government needs to spend about $7 billion over 20 years to improve the country’s locks and dams.

“We need, as a country, to summon the will to look at this as an investment and not just a spend,” Calhoun said. “These projects take a decade or so to complete. You can’t wait till you have a problem to start to fix it. You need to get ahead of the curve.”

Even if there were no barge traffic, companies like Cargill would still get their products to market. The company ships by trucks, rail and barge, but prefers that all three modes of transportation be robust in order to maintain healthy competition and keep shipping costs down.