The Directive defines the category "lake" as "a body of quiet superficial inland water " (Article 2) and specifies a lower limit of 0.5 km2 when establishing its rates (Annex II). At the level of Spain and based on preliminary CEDEX criteria, all those lakes with an area of ​​more than 50 ha (0.5 km2) or all those with an area of ​​more than 8 ha and exceeding 3 m in depth are included as bodies of water. The Agency through two agreements with research centers has proposed as bodies of water that could be assimilated to the category of lakes: 1 - Lakes and ponds of more than 0.5 ha of surface located at altitudes above 800 m and lakes below this level with a depth of more than 6 m (agreement with the CEAB-CSIC; Agency, 2003d). 2 - Wetlands located at altitudes below 800 and with a depth of less than 6 m (agreement with the UdG; Agency, 2004d). Also included in this category are the reservoirs of the inland basins of Catalonia.

In order to develop the Article 5 of the Directive, it is necessary to define in advance the basic river network of the demarcation on which the water bodies will be delimited. To do this, the river network extracted from the 1:50,000 scale topographic base of the Cartographic Institute of Catalonia (ICC, 2002) was used. On this basis, some background has been taken into account and some criteria have been applied that have served to establish the definitive scope of the river network. Background: These backgrounds are based on the following three considerations and sources: - Water Framework Directive: the classification of rivers according to system A of the Directive considers rivers with a drainage basin equal to or greater than 10 km2. - Centro de Estudios Hidrográficos del CEDEX: has restricted the basic hydrographic network based on two conditions: (i) drainage basin equal to or greater than 10 km2; and (ii) an average annual contribution in natural regime greater than 3.15 hm3/year (100 L/s). - Reference stations: regardless of the flow and the drained basin area, the river sections where reference stations are used to determine the reference conditions of certain river types have been considered.