Heavily modified water bodies (HMWB) are surface waterbodies that have had their physical characteristics, or hydromorphological conditions, modified by engineering works for drainage or development.
Water bodies are modified for power generation, the creation of dams for water supply, flood defences, industrial activity, to improve drainage and for navigation. These modifications prevent the river or waterbody functioning in its natural state and may impact on the diversity of fish populations and invertebrates that can live there owing to impacts on the natural conditions. This means that these waterbodies cannot reach the good ecological status required for fish and invertebrates under the Water Framework Directive. These circumstances are recognised in the Water Framework Directive and such waterbodies are designated as heavily modified and required to achieve Good Ecological Potential rather than good ecological status that needs more natural conditions. Under Good Ecological Potential standards not impacted by the modification still needs to be achieved such as good chemical and nutrient status.
Recent EU guidance to help Member States designate water bodies that have been modified has resulted in Ireland re-designating many of its water bodies.
Using the 11 step process of the new guidelines that includes (a) waterbody characterisation tests, (b) designation tests and (c) the assessment of potential objectives, Ireland has designated a total of 466 waterbodies as heavily modified. The largest contributor is the arterial drainage of rivers.
The EPA is holding a public consultation to seek views on the designation from which the EPA will make recommendations to the Department of Housing, Local Government and Heritage on the final designations for inclusion in the next River Basin Management Plan cycle
A total of 433 river, 20 lake and 13 transitional and coastal (TRAC) water bodies have been identified as Heavily Modified Water Body candidates
List is here: