Deep in the Brazilian Amazon River basin, scientists led by the Smithsonian's National Museum of Natural History fish research associate C. David de Santana discovered a small, river-fed lake filled with more than 100 adult electric eels, many of which were upwards of 4 feet long. On its own, this was an intriguing discovery, electric eels—a type of knifefish rather than true eels—were thought to be solitary creatures.