Tidal marshlands in the upper estuary ecotone provide essential habitat for juvenile salmonids. In this environment, salmonids grow rapidly and acclimate to saltwater. Worldwide, tidal marshes have been diked and drained to provide agricultural and residential land. Tide gates are one-way doors integrated into dike systems that prevent saltwater flooding and allow upland drainage to the estuary during low tide. By preventing tidal exchange, tide gates have significant upstream effects on water temperature and chemistry, plant and animal community structure, and geomorphology. Since they are closed most of the day and may be difficult to pass when open, tide gates may act as fish passage barriers for juvenile salmonids. They may also affect juvenile salmon migration timing by altering environmental variables that influence emigration rate in upstream habitats. We conducted our research in Coos Bay, one of the many Oregon estuaries with extensive use of tide gates.