Ballinacarraig weir

Barrier Mitigation

The mitigation to allow fish to pass barriers and reconnect rivers

A barrier is anything in a river that might stop a fish from passing, migrating or slow it down on the way up-river. Barriers can be natural or man-made and include weirs, bridges, waterfalls, culverts, debris blockages and hydroelectricity generating stations. Barriers can disconnect the natural flow of rivers and the sensitive ecosystems that exist in and around our rivers.

Bretts Weir National Barriers Programme

Inland Fisheries Ireland have a National Barriers Programme to identify and map barriers around the country. This helps Inland Fisheries Ireland to prioritise which barriers are the most difficult for fish to move past and which projects will have the greatest impact on allowing fish movements to the greater catchments. The National Barriers Programme specifies the most appropriate management approach which may involve removing the barrier from the river, removing a section of the barrier or creating a structure on the barrier called a fish pass. 

National Barriers Programme Deel

Carrying out Barrier Mitigation projects on man-made structures in river systems can be a complex process involving a lot of planning, research, surveys, consultation and innovation to identify the most appropriate management technique to adapt. This includes but not limited to:

  • The owners of any structure, fishery and associated landowners have to be identified and consulted. 
  • Surveys must be carried out on existing natural environment including river flows, gradients, fish communities, sensitive species, underwater substrate, the wider riparian zone including potential upstream and downstream impacts.
  • Studies must also be conducted to determine any potential impacts on safety, the environment, pollution, flood risk, archaeology, national monuments and on the social aspects of the river. 
  • Design options have to be developed to find out what the most appropriate solution for fish passage is.
  • Value to conservation and the long term sustainability of the project is considered against the expected cost of the project.


Barrier to migration inland fisheries ireland

Please see below a videos of the Ahascragh barrier mitigation project that was recently  undertaken by Inland Fisheries Ireland.

We have introduced a series of scientific research papers and guidance materials. You can view our Research guidance and activities below.