Mayantuyacu river, Peru
A mysterious, four-mile long river, deep in the heart of the Amazon, is so hot that it boils. The river has long been a legend in Peru, but when geoscientist Andrés Ruzo’s heard about it, he thought such a phenomenon couldn’t possibly exist because the Amazon basin is far from volcanic activity. The river boils because of fault-fed hot springs. Parts of the river are so hot that any animals that falls in boils instantly. (source)
Boiling River, Yellowstone National Park
The Boiling River is created where a large hot spring enters the Gardner River, allowing the hot and cool waters to mix into a temperature comfortable enough to bathe in.
Hveragerði Hot River, Iceland
Geothermally-heated river north of the town of Hveragerdi.
Firehole river, Yellowstone National Park
Excelsior Geyser Crater drains into the nearby Firehole River. The river was named by early trappers for the steam that makes it appear to be smoking as if on fire.