Tide gates are one-way doors integrated into dikes to prevent saltwater flooding and allow freshwater drainage into estuaries during low tides. These structures may act as barriers for migratory fish. We installed stationary passive integrated transponder (PIT) antennas in two streams: one with a top-hinged gate and one with no tide gate; and monitored smolt migration of coho salmon, Oncorhynchus kisutch. Our objectives were to: 1) describe the movements of smolts in a non-gated estuarine channel, 2) compare migration rate and behavior of smolts in a non-gated channel with those in a channel with a tide gate, and 3) identify tide gate conditions associated with smolt passage. We found that smolt travel time through the upper estuary was negatively correlated with fork length, and in the non-gated channel half of tagged individuals returned upstream one or more times. Smolt downstream migration peaked at sunset and coincided with flood tides. In the gated channel, smolt movement was predominantly towards the estuary (only 4% passed upstream) and occurred at greater gate angles and earlier in the day. Our results indicate that top-hinged gates interfere with the daily movements of coho salmon smolts in upper estuaries and alter their migration timing. The results of this study are interpreted within the context provided by a recent systematic literature review on tide gate upgrades and removal projects.