Rio Hamza, the river running 4km underneath the Amazon

Rio Hamza was discovered in 2011

Named after Dr Valiya Hamza, the scientist who was the head of the research team that found the subterranean river.

Same length as the Amazon, the world's second longest river

Trivia: the Amazon is the world's biggest river — every day 17 billion metric tons of the Amazon flow into the Atlantic Ocean - enough to supply New York City’s freshwater needs for NINE years. The force of Amazon's current is so powerful that it continues flowing 125 miles out to sea before mixing with the Atlantic salty water. That means sailors could drink fresh water from the Atlantic even before they could even see the South American continent.

Hamza much wider (200-400km) than Amazon (1-100km)

Both flow into Atlantic, Hamza discharging deep underground

Hamza runs 4 km (13,000 feet) beneath the Amazon, mostly vertical to about 6,500 feet deep, then changes direction and becomes almost horizontal at greater depths.

Average flow is only 2% of the Amazon