A modification of the inclined-screen trap was constructed to capture and facilitate processing of runs of salmonid smolts in large rivers. Modifications included a hanging inclined screen, a floating catch barge, and a fish sorter. Two such traps operated in the Little Manistee River in northwestern Michigan caught and held up to 2,500 steelhead (Salmo gairdneri) smolts per night. By sampling only a portion of the total river flow and using pipe weirs to guide smolts toward the two traps, we successfully sampled the smolt migration during periods of fluctuating water levels and debris content. It was estimated that our trapping scheme caught 42% of the steelhead smolts, 31% of the chinook salmon (Oncorhynchus tshawytscha) smolts, and 22% of the coho salmon (O. kisutch) smolts migrating downstream.