Amongst Americans, there's a common view that river monsters live elsewhere – in deep, wide rivers zig-zagging across foreign, untamed lands. Think vast Eurasia. And it's true, the supercontinent is home to some seriously ginormous freshwater fish. Beluga sturgeons, which live primarily in the Caspian and Black Seas but sometimes swim up their adjoining rivers, can extend over twenty feet in length and weigh more than 2,000 pounds! The species rivals the great white shark for the title of largest actively predatory fish. Further south and east, the Mekong River is home to stingrays and catfish that regularly tip the...