Dozens of fish carcasses 13 of them Chinook salmon protected by the Endangered Species Act rotted in the sun Tuesday a couple hundred yards from a new $6.3 million structure that state officials built specifically to keep that grisly scenario from happening. Before the winter and spring flood season this year, engineers completed work on the new fish passage along the Fremont Weir, a nearly two mile-long concrete structure atop the Yolo Bypass.