Let’s celebrate migratory fish!

Saturday 21st May 2022 is World Fish Migration Day, a celebration of migratory fish, which occurs every two years. The River Dee is home to a wide variety of migrating fish, species such as the European Eel, Atlantic Salmon, and the Sea Lamprey that travel huge distances between the oceans and the river. Even on a smaller scale, resident fish, such as brown trout, migrate up and downstream during the year. Completing this migration cycle is key to flourishing populations of wild fish and a healthy River Dee.

Unfortunately, migratory fish are in trouble. A 2020 technical report from WWF and IUCN found that migratory fish have declined by an average of 76% globally and 93% in Europe.  These statistics are reflected in populations of migratory species in the Dee.

The reasons for these declines are numerous, each coming together to cause these rapid declines.

Barriers to migration

Human built obstructions stop many migratory species from reaching long sections of the river. Even when passable, the extra energy required can reduce fishes’ ability to spawn or make them more prone to predation. The Dee and its tributaries have hundreds of barriers to migration, including very large ones such as Erbistock Weir, Horseshoe Falls and Bala Sluice gates.


Pollution comes in many forms, nutrients, plastic, hydrocarbons and sediment.  All of these and more are found in the Dee coming from a variety of sources including sewage treatment works, agriculture, and road drains. These pollutants change the ecology of the river, causing reductions in river invertebrates and macrophytes. The very food and shelter required by migratory fish. 

Habitat loss:

All migrating fish have specific habitat requirements to complete their life cycles, such as clean spawning gravels, instream cover or deep pools. Human activity, such as straightening watercourses or excessive tree removal has made our rivers more uniform, removing many of these smaller niches.

Environmental Flows

Salmon stuck at Erbistock Weir during low flows

A natural flow regime is important for migratory fish. To ensure the Dee provides adequate drinking water the Flows of the Dee are some of the most heavily managed in Europe. Loss of periods of high water (spates) and rapid changes in flows can disrupt migrating patterns, making it harder for migrating fish. 

The Welsh Dee Trust are working to tackle all these problems:

  • Our ‘Restoring River Habitat’ programme removes barriers to migration and improves habitat.
  • Our ‘Water Wise Farming’ programme helps farmers identify and stop sources of pollution.
  • Our ‘It shouldn’t be in the Dee’ programme supports communities to identify and tackle sewage, plastic and highway pollution.
  • Our ‘environmental Flows’ programme is standing up as the voice for wildlife in ensuring that the managed flows of the Dee work for nature.

Each programme is delivering individual actions which combined together will create a flourishing environment in which migratory fish can survive.

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