From the BBC:
The money will fund water pumping and purification, as well as food deliveries to towns cut off by the drop in river levels.
The Brazilian air force has already flown 500 tonnes of supplies to areas that usually depend on water transport.
The River Amazon at Manaus has fallen to its lowest level since 1963.
Scientists say the region is facing its worst drought since that year.
In Amazonas state 27 municipalities have declared a state of emergency because of the dry spell.
Several tributaries of the Amazon have almost completely dried up, paralysing river transport and the fishing industry.
The rainy season in the region usually begins in November.
The Peruvian Amazon, 2,000km (1,240 miles) upstream has also been affected.
Environmental groups say severe droughts are likely to become more frequent in the Amazon as a result of global warming, putting further strain on the rainforest.
The Amazon is the world's second-longest river, after the Nile, but discharges far more water from its mouth and drains more territory.