From space, the earth looks blue. Over 70 percent of the planet’s surface is covered by water, the majority of which is in the world’s seas and oceans. Half the world’s population lives within 100 km of the sea, and three-quarters of all large cities are located on the coast. However, the seas and oceans are under increasing pressure from pollution. Much of this pollution comes from urban centres, and it creates environmental problems which threaten the viability of the cities themselves. Local action to address the pollution of coastal areas is vital if cities are to take full advantage of the economic, social and environmental benefits of their locations. Since most of the earth’s water resources are shared by two or more countries, coordinated action, locally, nationally and internationally is equally important.