Greater clarity for future environmental management of Heavily Modified Water Bodies
- Published on: 18 December 2025
- Last updated on: 18 December 2025
Following a series of detailed technical assessments and public consultations, Ireland is designating 466 water bodies as Heavily Modified Water Bodies (HMWBs) in order to bring clarity to their future management.
HMWBs are rivers, lakes, estuaries or coastal waters that have undergone significant physical changes in order to provide important benefits to society, such as water storage and regulation (e.g. for drinking water), flood protection, the urban environment, arterial drainage or navigation.
These new designations will provide valuable clarity on both the management of these water bodies and the environmental targets applied to them, and are also expected to support a forthcoming review of arterial drainage practices, as committed to in the Water Action Plan 2024.
In designating the water bodies as ‘heavily modified’, the Minister of State for Nature, Heritage and Biodiversity, Christopher O’Sullivan TD, said:
“By designating these water bodies, we’re recognising that they need to be managed differently. They have been modified in the past in order to provide a societal benefit like protecting property from flooding or providing drinking water, so they should be subject to environmental objectives that ensure they are managed to the highest possible standard in that context. Our ambition for the ecological condition of these water bodies and their biodiversity remains high and there is much that can and will now be done to improve their value for nature on foot of these designations.
“Furthermore, the review of arterial drainage practices committed to in Water Action Plan 2024 will also be an important step in ensuring that Ireland meets its objectives on water quality and freshwater biodiversity.”
The newly designated Heavily Modified Water Bodies include 433 river reaches, 20 lakes and 13 estuarine and coastal waters, and are a lower proportion of our total number of water bodies compared to other EU Member States.
The designations were made following a technical review by the Environmental Protection Agency and further analysis by the Department of Housing, Local Government and Heritage. The assessments considered factors such as, the extent of physical modifications, the feasibility of restoration, the societal use of the water bodies and the availability of feasible alternatives.
For HMWBs designated due to past arterial drainage works, designation will make it necessary to ensure that drainage maintenance practices are environmentally sustainable while also continuing to protect over 180,000 hectares of agricultural lands, 13,700 residential properties and up to 9,300 commercial properties from flooding risk.
ENDS
Notes to the Editor
Examples of Heavily Modified Water Bodies:
Example A: River stretches that undergo drainage maintenance works. Historical drainage schemes, currently maintained by the Office of Public Works (OPW), provide flood protection for thousands of hectares of agricultural land and commercial and residential properties, as well as important infrastructure such as roads. The drainage maintenance activities can, however, affect the natural ecology of these stretches of river. The designation of the rivers within these schemes as HMWBs recognises this and applies appropriate environmental targets that are aligned with the benefits they provide.
Example B: Provision of drinking water. In some cases, a drinking water reservoir may be created by placing a dam on a river. This modifies a portion of the river to form a lake. The modification of the river is necessary to provide drinking water but it can also affect the natural ecology of the river. Designating that portion of the river as a heavily modified lake means that alternative achievable environmental targets are now set that take the modification into account. For example, Poulaphouca Reservoir in Co. Wicklow is an example of a heavily modified lake. The Reservoir was formed by damming the River Liffey over 80 years ago to facilitate the supply of drinking water and hydroelectric power.
Heavily Modified Water Body list – The list of 466 water bodies designated as Heavily Modified Water Bodies and a post-public consultation report can be found on the Government online public consultations page at here.
Third Cycle of Water Framework Directive – Under the EU Water Framework Directive, Ireland is required to produce a river basin management plan every six years to protect and improve water quality. The current plan (Water Action Plan 2024) covers the period 2022 - 2027. This plan sets out the environmental targets, and associated actions, for water quality to be achieved by 2027. The plan also identifies the bodies responsible for implementing these actions.
Water Body – A water body is the basic assessment unit used in the Water Framework Directive to check compliance against the environmental objectives that have been set. Water bodies can be lakes, estuaries, coastal waters or reaches of a river. Generally, rivers are made up of several water bodies, however, smaller rivers may sometimes constitute a single water body.
Action 3.10 of the Water Action Plan 2024 – Action 3.10 of the Water Action Plan 2024 relates to the designation of HMWBs and states: “The Minister for Housing, Local Government and Heritage will undertake a short public consultation before deciding whether to designate or de-designate water bodies as HMWBs. There were 466 water bodies, which the EPA has found to meet the criteria for designation. The Minister will take into account the recommendations of the EPA and the key concerns raised in the submissions to the consultation process.”
Heavily Modified Water Bodies (HMWBs) – Water bodies (rivers, lakes, estuaries or coastal waters) that have had their natural flow, form, or function (hydromorphology) altered to serve a beneficial specified use, e.g. impoundment of a river to create a drinking water reservoir. The modifications to the water course can affect the ecology; therefore, HMWBs are unable to reach the WFD objective that applies to natural water bodies (Good Ecological Status), instead, they have an alternative objective of Good Ecological Potential (GEP). GEP is a more realistic objective, taking into account the modifications necessary to provide the societal benefit of their specified use.
Hydromorphology – The subject of hydromorphology deals with the flow, form and function of a water body. In essence it deals with the physical habitats and processes that occur within a water body. A healthy hydromorphology is needed to support a healthy ecology and environment. Examples of hydromorphological features are, the flow rate of a river, or the structure of its banks and bed.
Placing dams in rivers or abstracting significant amounts of water for drinking water supply can affect the hydromorphology and ecology; but if these activities are of benefit to society, and no feasible alternative exists, then the water body can be deemed to be heavily modified.
More information on each HMWB can be found on www.catchments.ie.