Their dung consumes the oxygen around it, creating lethal pulses of suffocating water. At first, Chris Dutton and Amanda Subalusky had no idea why the fish were dying. At a bridge on the border between Kenya and Tanzania, they noticed that whenever the Mara River rose by a few feet, dead fish would wash up on its banks, sometimes in the thousands. Storks, vultures, crocodiles, and hyenas made shor