Pretty simple, Piper, those poor Green River smolts have to migrate through and feed in the most polluted and industrialized waterway in the state. The one's that don't pick up terminal liver disease from eating critters contaminated with arsenic, anthazene, chrysene, etc. are going to get pushed up against a vertical rock wall by a cormorant or grebe and eaten, or they are going to be killed from the shock waves produced by pile driving. No habitat=no fish