World Fish Migratory Day (WFMD): a day celebrated with the aim of raising global attention about the need for restoring river connections for migrating fish to achieve healthier fish stocks and more productive rivers.

In the Forth District, 5 of our 10 major river systems have a series of man-made barriers built across their widths (such as weirs). Though many of the weirs have lost their original purpose, they still act as a barrier, preventing migratory fish like salmon, sea trout, eels and lamprey from getting up the rivers and making the most of breeding or feeding habitat upstream. We have started on the long and difficult road of getting these barriers removed or adapted so that fish can go past them.

There are many different types of fish pass that can be used in different circumstances. In the majority of cases so far, technical solutions have been used – where fish locate a chute somewhere across the weir width. These can work for salmon and larger trout, but other fish species struggle to swim against the turbulent flow – extra provisions have to be made for eels and lamprey and perhaps even separate fish passes put in for these species. Consideration is not given to young salmon and trout on their downstream migration to the sea, and they are often damaged by this process.
It’s well established that technical solutions also fail to return natural processes to rivers. For example, sediment transport downriver is vitally important as gravel is required habitat for invertebrates and salmonids, without which, they would not be able to reproduce.
image shows a stepped weir with water rushing downstream, and on the right hand side a structured corridor with water travelling along it, a fish pass for fish to travel along and reach upstream.

Above, a technical fish pass (on the right hand side).

Even rock ramps, which are a more natural solution, may not be completely passable 100% of the time. Rock ramps involve building up the bed with rocks downstream of the weir so that fish can swim up a lower gradient river. The rock have to be embedded in the substrate to prevent them washing away.

Image shows trees either side with a river at the centre, with layers of rocks and gravel creating smaller corridors of water and pools joining these which allow fish to travel along the river.

Above: A semi-natural rock ramp.

With few exceptions, complete removal of the obstruction provides the most benefit in terms of returning the river to its natural function. This also benefits habitats supporting biodiversity. With the advancement of climate change and further decreases in overall biodiversity, these are the types of processes that provide rivers with their natural resilience to weather change and provide the best homes they can for wildlife. Use the slider on the images below to see the visual difference in a river before weir removal and what one looks like following weir removal.

A weir before removal - facing a river side on, a clear barrier has created fast flowing water below it, and an impassable barrier for migratory fish who cannot move upstream because of this.
A natural river is shown, a 'wiggly' bend, with water moving freely underneath a bridge structure, and great fish habitat pictured.

Above:  A slider gallery showing a river before weir removal, and a river after weir removal. The second picture shows a much more natural river, with excellent habitat for fish and a ‘wiggly’, more natural shape seen after infrastructure removal.

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