Session A5: Weir Removal in Lowland Streams - The Ultimate Tool in the Fish Managers Tool Box

Abstract: Anthropogenic changes such weir construction in rivers are common problems in many developed countries and Denmark is no exception. Through centuries, the rivers have been populated with thousands of weirs for various purposes such as irrigation, abstraction, pumping, flood control, fish farming and hydropower. The consequence has been highly fragmented river systems and vast negative effects on fish populations including extinction. For decades remedial measures have been incremental in the form of building fish passages principally constructed for upstream migrants. However, many places the consequences of weirs on fish populations reach far beyond the fish passage problems and hence the positive effect on fish populations has been limited. In the last decade we have run a number of programs targeting removal of various obstacles. In this talk we will present some of the results following weir removal and demonstrate the consequences for fish population both on a local and on a catchment scale. We suggest that removing weirs and dams do not require rocket science, is in many cases the best option, and argue that it in fact is possible many places given the right motivation and persistence