The UK Government is committed to ambitious targets to reduce carbon emissions. The large tidal ranges in estuaries on the west coast of the UK make the deployment of tidal barrages an attractive proposition, and repeated feasibility studies have been undertaken. No barrage scheme has yet been taken forward, and one factor contributing to this reluctance to proceed is the significant environmental impacts that could result from the barrage construction and operation. This paper provides a detailed review of the current understanding of the potential ecological and social impacts of tidal barrages, including a case study of La Rance in northern France, and a discussion of strategies for mitigating barrage impacts. The review considers how more comprehensive ecological modelling could reduce uncertainty in predicting the impacts in specific estuaries, and discusses the use of Multi-criteria Analysis and ecosystem valuation as tools for evaluating the disparate costs and benefits of barrages schemes.