This Tri-State Steelheaders project completed flood control measures on Mill Creek in Walla Walla included a diversion dam, storage reservoir, and a 6.7 mile long flood control channel, of which 2.5 miles is a concrete flume. This project completed designs and specifications for fish passage improvements at each end of the concrete flume based on design testing in a scale model of the channel, then implemented those designs. These flume transitions were identified as barriers in the Mill Creek Barrier Assessment completed in 2009. Concrete at each end of the flume was retrofitted with resting pools and with roughened concrete that simulates a cobble bottom channel to improve high flow passage. Reconfigured baffles in the center of the channel improve depth problems associated with low flows. The flood control channel creates water quality problems and presents a series of complex fish passage barriers. ESA listed steelhead, and bull trout, and reintroduced spring Chinook utilize the flood control channel during migrations. Returning adults encounter flow-dependent passage problems associated with channel spanning weirs, light attraction barriers (in the underground sections), and a lack of resting water in the concrete channel section, among other problems. Juvenile fish encounter low spring flows and high water temperatures in late spring. Often by mid-May adults and juveniles become trapped in the flood control channel where they experience lethal temperatures. Many of these passage issues are considered imminent threats in the Snake River Salmon Recovery Plan. Mill Creek, upstream of the flood control project, is a critical and under-utilized area for spawning and rearing of ESA listed species, and provides for an important recovery opportunity for those listed fish, as well as good habitat for other native fish and reintroduction efforts for spring Chinook.