In-stream barriers are controversial features in rivers, because they impede the movement and production of native and recreational (desirable) fishes, while their removal can permit the dispersal and proliferation of invasive species. Selective fish passage can eliminate this controversy by restoring movement for desirable fishes while preventing the movement of invasive species. Manually sorting fishes to achieve this is selective passage is effective, but is labour-intensive and costly, which establishes a need to evaluate technologies where fishes are passively or self-sorted. I completed two experimental field tests to evaluate if passive sorting of desirable fishes from invasive sea lamprey (Petromyzon marinus) could be improved by manipulating discharge (high or low) through a size-selective fishway, and by manipulating the configuration of a funnel (curved or straight) separating sorting chambers within the fishway. Increased discharge and addition of a curved funnel did not improve passive sorting, but daily total catches of desirable fishes and sea lamprey differed between discharge treatments in ways that could create sorting opportunities. My findings support that identifying singular passive sorting mechanisms could be challenging, and that there may be more success in combining multiple sorting technologies within a fishway.