River Mieån

river pearl mussels.
Photo: Mathias Arnham

Mussel recruitment and cooperation

River Mieån flows from Lake Mien towards the Baltic Sea through a rift valley with varied terrain. The water is clear and contains both resident and migratory trout, as well as species such as sandpiper, whitefish, burbot, brook lamprey and eel. Common tern and Arctic char nest along the river, and otters are scattered throughout the area.

kilometer long

the number of environmental adaptations of hydropower

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area (hectares) biotope conservation

the number of migration barriers to be removed

The pearl mussel population in River Mieån is fragmented and has been declining since the 1970s. Low densities of trout and migration barriers threaten the survival of the mussel, despite good water conditions. Thick-shelled clams have recently been found but are also threatened by habitat degradation and barriers to host fish.

River Mieån is heavily fragmented by dams used for mills and hydropower, hindering fish migration and affecting the flow regime. Historical clearing of the river for rafting has concentrated water flow and led to erosion. Drainage, wetland draining and lake lowering have reduced the river’s water holding capacity, which is also exacerbated by climate change and low summer flows.

Drainage, wetland draining and lake lowering have reduced the river’s water holding capacity

Necessary improvements
Habitats and improved connectivity in the watercourse need to be improved. The whole water body needs to be addressed to create favorable conditions for species such as trout and pearl mussels. Several Natura 2000 sites such as Loberget, Ire, Grimsmåla and Långasjönäs are covered by the work. The conservation status of important species and habitats is classified as unfavorable.

Within the LIFE IP project GRIP on LIFE, a hydromorphological action plan has been developed for River Mieån, which together with a long-term management plan forms the basis for further measures. Karlshamn municipality is actively working on the restoration of cleared stretches and Tingsryd municipality is participating in the management of the watercourse. Fishing area associations run their own restoration projects, and the biosphere reserve Blekinge Archipelago implements measures in the catchment area.

River Mieån is part of the national plan for the greening of hydropower, where six plants will be adjusted for improved connectivity.

Improve Aquatic LIFE actions
Improve Aquatic LIFE plans to restore wetlands in the Ire Natura 2000 site to improve water retention and increase resilience to climate change. Two migration barriers will be removed and upstream and downstream biotopes will be restored to enhance the habitat of the river pearl mussel and trout populations.

As the conservation status of the pearl mussel and the thick-shelled mussel is critical, infestation of mussel larvae is also required to secure future populations. Improve Aquatic LIFE actions interact with ongoing initiatives to achieve favorable conservation status for species and habitats and the environmental quality standard good ecological status in River Mieån.

Survival of river pearl mussels depends on host fish

Barriers to migration

Removing migration barriers and opening up the river pearl mussel’s host fish, salmon and trout, will increase the species’ ability to reproduce. Barriers to migration come in many forms, from natural to man-made dams and power plants. In some cases, a good solution may be to build a wildlife passage to allow fish and other organisms to bypass the migration barrier.

River Mieån

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