Details are given of the growing worldwide interest in tidal renewable energy projects, including tidal stream devices and tidal range structures (i.e. barrages and lagoons), but the main emphasis in this chapter is on tidal range renewable energy structures. In investigating the hydro-environmental impacts of such tidal energy schemes, both for regional and far field effects, a 2D numerical model has been refined to predict the hydrodynamic impacts, including wake effects and flood risk and hazard impacts, and changes in the concentration distribution of conservative and nonconservative solutes, including primarily salinity, turbidity, fecal indicator organisms, and phosphorous and nitrogen levels. The model has been applied to a number of key sites and particularly in the Severn Estuary, UK, which has the second highest tidal range worldwide. The key schemes considered and reported herein include: (i) a series of lagoons along the North Wales coast and (ii) a barrage across the mouth of the Severn Estuary. The main findings are that: (i) two-way generation offers the best options for maintaining the current conditions in the region as closely as possible, (ii) boundary conditions need to be generated from the Continental Shelf, (iii) momentum conservation is crucial for turbine representation, (iv)lagoons interact with one another, reducing efficiency, (v) the design of turbine distribution is critical for optimum efficiency and minimal environmental change.