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Working Group ECOSTAT report on common understanding of using mitigation measures for reaching Good Ecological Potential for heavily modified water bodies - Part 1: Impacted by water storage

Hydromorphological alterations due to e.g. water storage with major impacts on the aquatic ecology are among the most widespread pressures on water bodies in Europe. Many of these impacted water bodies have been designated as heavily modified water bodies, and many are expected to need mitigation measures to meet the good ecological potential (GEP) and some possibly good ecological status (GES) to fulfil the requirements of the WFD. Among the core activities for the CIS WG ECOSTAT from 2013 onwards, have been to assess the comparability of GEP among countries implementing the WFD. The aims of this activity and hence this report have been to develop a suitable method for assessing comparability (intercalibration), learn from each other to ensure common understanding and emerging good management practice across Europe, as a basis for supplementary guidance on HMWBs issues. In other words; agree on a common understanding on environmental requirements for water bodies impacted by water storage. Several workshops have been arranged and a series of templates have been circulated to national management experts to get a comparison of available measures in mitigation libraries and use thereof. In the present report, the assessment of comparability is based on returned templates from 23 countries. Response is lacking from four countries while three countries have informed ECOSTAT that finalising and use of national libraries is still ongoing. The outcome has been a common terminology and some key findings regarding key ecological functions normally expected to be mitigated by measures in water bodies impacted by water storage to meet the requirements of GEP.