Hellsten S, Willby N, Ecke F, Mjelde M, Phillips G & Tierney D (2014) Water Framework Directive Intercalibration Technical Report: Northern Lake Macrophyte ecological assessment methods. European Commission. JRC Technical Reports. Publications Office of the European Union. http://publications.jrc.ec.europa.eu/repository/handle/111111111/30713
First paragraph: The European Water Framework Directive (WFD) requires the national classifications of good ecological status to be harmonised through an intercalibration exercise. In this exercise, significant differences in status classification among Member States are harmonized by comparing and, if necessary, adjusting the good status boundaries of the national assessment methods. Intercalibration is performed for rivers, lakes, coastal and transitional waters, focusing on selected types of water bodies (intercalibration types), anthropogenic pressures and Biological Quality Elements. Intercalibration exercises were carried out in Geographical Intercalibration Groups - larger geographical units including Member States with similar water body types - and followed the procedure described in the WFD Common Implementation Strategy Guidance document on the intercalibration process (European Commission, 2011).