The Amazon, the world's biggest river, is at its lowest level in over 40 years near its source in northeastern Peru, causing havoc in a region where it is used as the only form of travel, authorities said.

According to officials in Loreto province, the Amazon on Tuesday in the northeast city of Iquitos fell to 105.97 meters (347.67 feet) above sea level, 50 cm (1.6 feet) lower than it was in 2005, so far the lowest reference point in four decades.

Low levels have brought economic havoc in areas of Peru that depend on the Amazon for shipping, by denying boats a navigable river as well as usable ports and harbors.

At least six boats became stranded for lack of river flow over the last three weeks and several shipping companies have been forced to suspend service, said regional civil defense chief Roberto Falcon.

River trips between Iquitos and other Amazon towns that normally take around 12-15 days now last twice as long, officials said.

According to the national meteorological service, the level drop -- which is forecast to slide another 20 cm (0.6 feet) until mid-September -- has been caused by a lack of rain and high temperatures in the region.

The Amazon is the second-longest river in the world, after the Nile, but discharges far more water at its mouth than any other.

It also drains more territory than any other, from Colombia, Bolivia, Ecuador, Peru, Paraguay and Venezuela before running across Brazil and into the Atlantic.