The ecological effects of tide gates are thought to be sufficiently understood to justify estuary restoration involving removal or upgrades of aging structures with the goals of improving fish passage and estuarine habitat conditions. However, whether tide gate upgrade or removal affect salmonid passage, growth and survival, and habitat quality, lacks clear answers in the primary literature. To address this paucity of information, we conducted a systematic review of the primary literature and of tide gate related project reports. We used a multi-faceted approach to knowledge synthesis, including review of relevant scientific literature, agency and non-agency reports on tide gate projects, and inquiries to state and federal agency staff working on estuary restoration in the Pacific Northwest region. Some of our findings indicate that: a) tide gates limit connectivity in a way that negatively affects fish passage, community composition and water quality, b) all tide gates have some impact on fish, even those labelled “fish friendly”; c) tide gate removal or upgrade projects produce very variable outcomes because not only the design of the gates may affect results but also their location and installation in the channel network; d) fish passage improvement is only one of the four main objectives of tide gate projects, the others are fish nursery habitat improvement and expansion, flood damage reduction and infrastructure protection; e) tide gate projects are only the first step in improving ecological conditions in fish migration corridors. The data and reports we summarized provide ample sources of the raw materials needed towards the development of guidelines, based on ecological and econometric principles, to determine the costs and benefits of various types of tide gate removal or replacement and estuarine restoration projects.