The mighty Mississippi isn't looking quite so mighty these days.

When you look closely, it's possible to see exposed sandbanks at the river's edge and occasionally in mid-stream.

That's because a lack of rainfall in the Midwest is starving the river - a vital US trade route - of water.  And when the level goes down prices go up.

Barge owners can't fully load their vessels for fear they'll get stuck in the mud. They have to travel light and moving barges half- or three-quarters full eats into profits and drives up costs.

In August, the river was so low at Greenville, in the state of Mississippi, that it became impossible to navigate for a while. 

About 100 vessels came to a halt at an estimated cost to the economy of at least $3m a day - costs that will have to be passed on to the consumer somehow.

Dan Overbey manages South East Missouri Port (SEMO), one of many tiny ports scattered along the river.

"Between the drought and its effect on farm products prices, and also the river situation and the transportation cost, I think it'll be felt ... it's something we'll get past but it’s going to be a problem in the short term and it's going to affect some of the numbers," Overbey said.

All along the Mississippi the falling river level has got port workers like Paul Koch of Girardeau Stevedores worried.

"If we don't get no water pretty soon and it gets cold its going to freeze over and you isn't going to move nothing out here. We will be shut down then," Stevedores said.

US Army Corps of Engineers

The US Army Corps of Engineers is charged with keeping the dredged deep water channel open right along the Mississippi.

In the Trail of Tears Park, outside St Louis, Missouri, the Corps of Engineers has been using the oldest piece of serviceable equipment in the US Army - the dredge potter - to suck up the unwanted silt and deposit it outside the navigation channel.

The Corps has measured the Mississippi at just over two metres in this area - a year ago it was just over eight metres.

Lou Dell'Orco's in charge of 600km of the Mississippi.  He has 27 years' experience managing the river for the Corps of Engineers.

"We take surveys and go out and use survey boats so we can provide the information to industry and they can load their barges accordingly," Dell'Orco said.

And with the forecast showing little sign of any serious rain in the Midwest in the immediate future, that's information everyone along the Mississippi is relying on more than ever.

Breaking news

Weather forecasters say rainfall from the approaching Hurricane Isaac may help raise the water level in the Mississippi a bit depending on where he hits, but it's unlikely to make the drought problem go away overnight.