An extensive new port is being constructed at Vuosaari, on the outskirts of Helsinki. A Natura 2000 site important for wild birds is situated just outside the harbour. As a result, nature conservation and economic interests have come into conflict, which has resulted in long and cumbersome decision-making processes both at the national and the EU level. The case highlights many principles and key provisions in the Habitats and Birds Directives, such as the precautionary principle, the role of assessment and decision making, the delimitation of sites and the cumulative effects of projects. The duty of the Supreme Administrative Court to request an opinion from the European Court of Justice is also one of the key issues. This article examines the implementation of the Habitats and Birds Directives and the interpretation of some key provisions in light of EU case law.