A clear delimitation of coastal waters facing the EU environmental legislation: from the Water Framework Directive to the Marine Strategy Framework Directive

The definition of coastal waters in relation to the European Union (EU) environmental legislation was clearly stated in the Water Framework Directive. In compliance with this Directive, most of the EU Member States have delineated their coastal waters’ boundaries. However, these delineations are not as complete and homogeneous as could be expected. Hence, there is a need for a comprehensive and unambiguous delimitation of European coastal waters. This paper aims at bridging this gap, providing a pan-European mapping of coastal waters, covering 553,817 km2 in 30 seaside countries, 340,524 km2 of which pertain to the 22 EU Member States connected to the sea. For this purpose, a comprehensive geographical analysis of the national baselines and transitional waters distribution was performed. A pan-European baseline of 63,340 km was delineated, together with the coastal waters delimitation (the final GIS layers are provided as supplementary material of this article). The results show significant differences between the available national declarations of coastal waters and the areas identified in this work (almost 12% of the compared area), the former defining an additional 29,337 km2 of coastal waters with respect to the latter. The largest deviations seem to be due either to misinterpretations of the definition of coastal waters, or to one-sided national modifications. A clear identification of European coastal water boundaries is crucial for the Water Framework Directive and the Marine Strategy Framework Directive implementations, which depend on an accurate ecological/environmental assessment of those waters.