The installation of wind farms is considered a key step towards the provision of sustainable energy supply in the UK. Offshore wind farms offer a great potential in terms of availability of resources in terms of space and energy with the minimum of impact on human activity. A growing body of evidence, however, suggests that the construction and operation of wind farms are likely to pose a risk to offshore wildlife. As such, these wind farms must undergo detailed environmental impact assessment prior to installation to determine their impact on marine fauna. In this paper, we discuss the construction of a large UK wind farm, for which a comprehensive noise study was produced reviewing its impacts and the calculation of their severity. The impacts on underwater wildlife considered included lethality and physical injury, auditory effects and behavioural avoidance response. The use of an underwater broadband noise propagation model which has been implemented as software, and which has been validated for shallow water is described. The range of effects of unweighted, dBht(Species) and M-weighted Sound Exposure Level were calculated for a variety of appropriate species with this software. This software tool was used interactively by the engineers, regulators and marine specialists, and it offered the constructor the ability to assess and minimise the development's potential for environmental impact from an early point. This allowed the developer an accurate impression of the likelihood of gaining consent for the project and provided a direction for the best way to minimise or mitigate the introduced noise.