Such a prospect seems incredible in Manaus, a Brazilian port city where both the Amazon and Rio Negro are more than five miles wide and 300 metres deep. At more than 1,000 miles from the sea, the two streams can be navigated by oceangoing ships and already dwarf every other river in the world in terms of volume.
But last year the worst drought in more than a century hit the Amazon basin, drying up tributaries more than a mile wide and prompting Brazil to declare a state of emergency across the entire region.
Tens of thousands were cut off as rivers that are the main means of transportation were turned into mudflats and grasslands, leaving boats stranded among millions of rotting fish on the baked mud.
Locals hoped the drought was a once-in-a-generation event, but already there are signs that the extreme conditions of last year are returning. In the Acre region close to Brazil's borders with Bolivia and Peru, where last year's drought began, sandbanks have started appearing in rivers which are normally larger than any of their European counterparts.
Such conditions usually occur only at the end of the dry season three months from now, but this year Acre went without rain for 40 days in June and early July, a circumstance almost unheard of. The government's technical foundation in Acre said the vegetation was so dry that there was a serious danger of forest fires.
The blessing of the rivers came at the start of a conference examining the deterioration of the Amazon basin that brings together religious leaders, politicians and scientists aboard a fleet of boats anchored in Manaus, the Amazon's main city.
Brazil's environment minister, Marina Da Silva, said the drought was linked to record sea temperatures in the south-west Atlantic and Gulf of Mexico that had also contributed to last year's record Atlantic hurricane season.
But the destruction of the rainforest by illegal loggers has also been named as a cause, as rivers become choked with silt swept from the denuded land.
Ecologist Carlos Rittl said the continued removal of trees was a crucial factor in the drying of a region that has already lost 17% of its forest cover. "The science shows that 50% of the rain comes from the trees recycling the water through evaporation, which creates more rain. If you lose the trees you lose the rainfall. It cannot continue like this," he said.
Ms Da Silva said Brazil was determined to stamp out illegal logging and the destruction of the forest for ranching and growing soya beans. A clampdown over the past year has resulted in 300 people, including corrupt officials, being arrested, while 1,500 businesses have been shut down and 600,000 cubic metres of illegal logs seized.