The Water Action Plan 2024 published by my Department sets out a roadmap to restore Ireland’s water bodies to ‘good status’ or better and to protect water from any further deterioration. However, some of our water bodies have been physically modified in the past to serve a beneficial specified use to society, e.g. flood protection and the provision of drinking water. The modifications required to achieve these benefits may alter the natural flow, form or function (hydromorphology) of the water body, such that it is no longer in a natural state. These modified water bodies may not be capable of achieving the same environmental targets as their natural counterparts, e.g. if the river is constrained by urban area. In these cases, the water bodies may be designated as Heavily Modified Water Bodies (HMWBs), as provided for under Article 4(3) of the Water Framework Directive (WFD - 2000/60/EC).
The River Tolka has been proposed for designation as heavily modified due to both the presence of engineered flood defences in Meath and Dublin and being partly in an urban setting. A significant level of flood protection is provided by the flood relief schemes to both rural and urban lands (e.g. Blanchardstown and Mulhuddart), including the protection of over 1,600 properties, public infrastructure and public realm facilities.
The flood relief schemes were implemented across three local authorities (Meath, Fingal and Dublin City) by the Office of Public Works. A range of alternative options were considered at the design stage of the River Tolka Flood Study, which was carried out in 2002. There is no known alternative solution that can provide the extent of flood defences required at this point in time and the removal of these schemes would also result in a risk to public safety. In addition, as the river corridor is confined by an urbanised ‘city’ environment, it is considered that the removal of these defences would not achieve significant environmental benefit (i.e. the river does not have space to return to its natural state).
The environmental objective for HMWBs is not a lower standard. Designation of water bodies as heavily modified acknowledges that there has been a modification for the purposes of a beneficial specified use, and that different, more appropriate environmental standards need to be applied. The proposed designation of the River Tolka would require it to be assigned a target of ‘Good Ecological Potential’. This reflects the best environmental target that the water body is capable of achieving while the modifications to support the specified use (in this case flood protection) are still in place.
As part of the Environmental Protection Agency (EPA) National Water Quality Monitoring Programme, the sections of the Tolka in question have been assessed as having ‘poor’ status. The EPA may provide any additional information required regarding their assessment protocol.
The EPA completed a public consultation on the designation process in 2022 and my Department undertook a further 8-week public consultation which closed on 23 May 2025. There will be no further public consultation prior to final designation. All submissions received during the consultation period will be considered.
It is important to note that this is an iterative process. HMWB designation is revisited in each river basin management planning cycle (every 6 years) taking into account new information, changed circumstances and the technical feasibility for restoring to natural conditions. Where these factors are favourable, HMWBs have the potential to be de-designated in future planning cycles.
