Weirs and barriers to fish migration


Weirs and barriers to fish migration

Under the EU Water Framework Directive, member states are required to improve the ecological status or potential of waterbodies. To that end, Inland Fisheries Ireland (IFI) has surveyed 19,200 structures in our rivers and identified 2,500 as being barriers or potential barriers to fish passage. These barriers are typically historical weirs, bridge aprons, culverts or other instream structures which were often constructed without the appropriate consideration of fish passage.

IFI is rarely, if ever the owner or responsible party for the management of these barriers but understand the impact of barriers to riverine ecosystems and the benefit which can be gained by improving fish passage. IFI has a statutory responsibility for the protection, management and conservation of Ireland’s inland fisheries resource and it is in this context that IFI has and continues to identify and address barriers to fish migration.

Francis O’Donnell, CEO of Inland fisheries Ireland said: ‘Barriers to fish passage will block fish from being able to migrate upstream and in turn will have an impact on the decline in fish populations if they cannot go upstream to spawn. Continuity in our rivers is critical for the free movement of fish and the wellbeing of our fisheries ecosystems. Most of the barriers that exist in rivers nowadays in Ireland were constructed during a time when fish passage was not taken into consideration. Over the past number of years IFI has led on or supported a number of projects to address fish passage at a number of major barriers. 10 barriers have been removed, another 30 other barriers were altered to improve fish passage.’

Improving fish passage at barriers is complex and involves co-operation and support from numerous stakeholders and the public. These projects also require significant resources and funding and are typically multi-phase projects which take a number of years to deliver. Projects are usually carried out over a five-stage process:

  • The first phase is identifying and communicating with key stakeholders such as weir and property owners, the various state agencies with responsibility for weirs/ rivers such as the OPW, local authority, ESB, NPWS and various Government departments to undertake a preliminary assessment of whether the project can progress to phase two.
  • Phase two involves securing appropriate funding and resources to deliver the planning phase of the project.
  • Phase three involves a wider consultation process including; environmental considerations, the development of design options and may also involve applying for planning permission. Design options for fish passage improvement at large weirs typically include; partial or complete removal, installation of a rock ramp type structure or the installation of a bypass channel or other fish pass.
  • Phase four is the application for funding for the construction phase.
  • Phase five is the delivery/ construction process to complete the project.

At the present time two fish pass improvement projects have been submitted for planning with a further five in the design stage that will be lodged for planning in due course.

Annacotty Weir

IFI has identified Annacotty weir on the lower Mulkear river as a significant barrier to the free movement of several fish species. The weir is a priority for fish passage improvement and IFI has begun preliminary works to initiate a project to address fish passage at the weir. IFI is engaging with the various state agencies and key stakeholders with the intention of progressing the project to the next phase. However, this is a complex project with numerous risks and the successful delivery of this and other such projects involves support from numerous stakeholders and the public.

Annacotty Weir web

David Mc Inerney, IFI’s Director in the Shannon River Basin District commented that ‘historical weirs such as Annacotty have impeded the movement of fish since they were built or modified. The fish pass in the weir helps some species navigate the weir at certain water levels but it is far from ideal. It would be a great success if all the stakeholders can support a project with the aim of making the wonderful river Mulkear once again easily accessible to all fish, as nature had intended.’

IFI is pleased to see the online public support for addressing fish passage at the weir and hopes that this momentum will support the delivery of improved fish passage at the weir.

The Mulkear is considered a very important river for a range of fish species including wild Atlantic salmon, sea, river and brook lamprey, wild brown trout and eels. The majority of the main river and it’s smaller tributaries in the catchment are designated as a Special Area of Conservation (SAC) under the EU Habitats Directive.

A previous IFI supported project involved the OPW decommissioning Ballyclogh weir which is located upstream of Annacotty weir. This resulted in the free movement of fish through this section of the river Mulkear. IFI has also previously made minor improvements to fish passage at Annacotty weir. This involved the fitting of eggcup-type structures to the weir face to assist lamprey movement over the weir. IFI is aware that these structures have degraded following several flood events.