Instream-river engineering structures, such as weirs, bridges, vehicle fords and culverts, can block or deter upstream movement of migratory salmon and sea trout, thereby preventing them from reaching their spawning grounds higher up in the catchment. On the Dee’s tributaries, there are approximately 30 obstructions to fish migration. Some are completely impassable to fish, whereas others are impassable in low flows; the latter can delay migration and have a knock-on effect of making fish more vulnerable to predators.

While these obstructions have been identified, the benefits of removing these obstructions or making them passable have not been determined. For example, removing an obstruction that is on a tributary with poor habitat for salmon, or that is located close to the headwater source, will offer a lot less potential for increasing fish production than removing an obstruction that is low down on a prime-quality tributary.

The Project Biologist will be assessing all of the obstructions on the Dee. By quantifying factors such as habitat availability and quality, obstruction passability, engineering works required and risks involved, we will have a clear working list for tackling these obstructions.

The assessment of the obstructions is almost complete, and removal of the  obstructions will begin in summer 2007.