10.4122/1.1000001316 Silva, M. Cardoso da Fl\303\264xo, V. Characterization of transitional waters in the context of the WFD - Case studies of Portuguese estuaries DTU Library, Technical University of Denmark (DTU) 2005 Estuaries Water Framework Directive Environmental indicators Nacional Laboratory of Civil Engineering, Hydraulics and Environment Department en Conference full text 10.4122/1.1000001315 application/pdf 1 In the European Union (EU) a first demanding Directive, associated with wastewater drainage and disposal was the 91/271/CEE concerning Urban Wastewater Treatment that imposes particular requirements when the receiving water bodies are estuaries. Further requirements were introduced by the Directive establishing a framework for Community action in the field of water policy (2000/60/EC) the Water Framework Directive (WFD). For the implementation of the EU legislation it is of key importance to develop a comprehensive methodology for the characterization of the pressures on water bodies and of their status. The method to compute the normalised indicators from the observations is described and tested, requiring the definition of assessment criteria and of an algorithm to transform the observed values, integrated in time and in space, into dimensionless values and, later, in the normalized indicators. The test was performed in three Portuguese estuaries, Tejo, Sado and Guadiana, with different characteristic and pressures. The issues of oxygenation and eutrophication were selected. Although the available data was not collected for the application of the methodology, it was still possible to define environmental quality classes for each system.