The possibility of massive exploitation of marine resources poses many problems in applying classical models of economic development. This article considers the coastal region as a non-homogeneous space, and proposes a series of concepts which are important in the process of economic development of the region. The components of the region, land and water, are allocated and distributed by Systems of property and exchange which are completely different the one from the other. The water body is rather a « common property resource », and it is in the nature of such resources that negative external economies (externalities) are in existence. Discussion focuses on the notion of externality and on the concept of conflict. A simple empirical model of conflict is proposed and is applied to the Puget Sound region of western Washington State (U.S.A.). The results of this analysis form the basis of a discussion of the problem of conflict resolution.