The Water Framework Directive (WFD) allows Member States to identify surface water bodies which have been physically altered by human activity and designate them as heavily modified water bodies (HMWB). If the uses of such water bodies (e.g. navigation, port or harbour, or flood defence) would be significantly affected by the mitigation measures required to achieve good ecological status (GES) and if no other better environmental options exist, then these water bodies can be designated as heavily modified and ‘good ecological potential’ (GEP) is set as an environmental objective.
WFD Northern Ireland Marine Surface Water for Heavily Modified Transitional and Coastal Water Bodies in Northern Ireland - 2015