But many non-human creatures also depend on the Colorado watershed, most of all the strange, hardy fish that prowl its turbid depths. This is the domain of the bonytail chub, the razorback sucker, and the Colorado pikeminnow, a six-foot-long predator that early anglers caught by tying fishing lines to their truck bumpers. The lower Colorado has the highest ratio of endemic fish in North America—meaning that six of its eight native species exist nowhere else on Earth.