Brazil has adopted emergency measures to deal with one of the Amazon region's worst droughts in decades.
Low water levels are making the river hard to navigate
Scientists say water levels have fallen to a 30-year low, creating difficulties for river transport - in many cases the only way of moving people and goods.
Many towns along the world's second longest river have declared alerts amid fears they could become isolated.
Experts are blaming climate cycles, not global warming, for the drought, which has also led to enormous fires.
Brazilian meteorologists think the weather in the Amazon is affected by sunspots and water temperatures in the Pacific Ocean - factors which vary in regular patterns.
The average low for the Amazon River is 17.6m (58.1ft). But, on Sunday, the water level was measured at 16.2m (53.5ft), according to Daniel de Oliveira of the Brazilian Geological Service.
The Amazon - which is a lifeline for those who live in the river basin - is expected to continue dropping until November, he was quoted as saying by the Associated Press.
There are reports that a fuel barge headed for the city of Manaus has been stuck for two weeks because of the low waters.
Last week, 16 people were killed in a ferry accident which the captain blamed on difficult river conditions.
The dry spell is also affecting Peru, where the Amazon River at the river port of Iquitos has seen a record low.
Iquitos is reported to be experiencing long delays in the delivery of food because the river has become difficult to navigate.