With last year's well-publicized shortages of truck and rail capacity, you might expect that 2006 would turn out to be a banner year for alternative transportation modes like barges. But it didn't quite work out that way. Freight traffic on the Missouri River, for example, plunged to less than 200,000 tons last year—the lowest level reported since 1951.

It seems Mother Nature was partly to blame. A scarcity of rain and snow in North Dakota, South Dakota and Montana in recent years led to the depletion of many northern reservoirs that feed the Missouri River, resulting in historic lows in river levels.

The impact was felt most heavily in the agricultural sector. The river's shipping season ended more than a month and a half earlier than average last year, forcing farmers to seek other transportation options at harvest time.