Background The Ulla river basin experiences different pressures that impact on aquatic species such as freshwater pearl mussel (Margaritifera margaritifera) and Pyrenean desman (Galemys pyrenaicus). Threats affecting these species include degradation of the river bed substrate, from dredging and siltation, degradation of riparian forest and difficulties for host species to move upriver (in the case of M. margaritifera). Both these species act as biological indicators for the overall state of the Ulla’s fluvial ecosystem and conservation actions that tackle threats to these species will have knock-on benefits for many other species living within the Ulla river basin. Objectives The overall objective of the LIFE Nature project is to help improve the conservation status of the freshwater pearl mussel and Pyrenean desman in the Ulla river basin, and establish suitable conditions for recovery of the original populations. This will be achieved by: increasing knowledge about the factors threatening both species; improving habitat factors associated with the decline of both species; implementing measures to recover the hydromorphology of certain sections affected by dams and drawdown flow, in order to foster natural dynamics of the freshwater pearl mussel and facilitate connectivity of potential desman population centres; reinforcing and reintroducing M. margaritifera in suitable areas of the river basin; improving the conservation status of riparian forest in the project area; and implementing best practices in the management of river and riparian forest habitats, as well as matters affecting river quality, such as phytosanitary, bed loads and particles. Expected results: Improved knowledge about the conservation status of the freshwater pearl mussel and Pyrenean desman populations and factors affecting their habitats (sources of pollution, riparian forest status), as well as threats to both species; Maintenance of sufficient genetic variability of pearl mussel populations to allow re-stocking with local specimens from the basin itself; Improved knowledge of the response of the Pyrenean desman to actions involving the elimination of barriers to natural river dynamics; Fostering the natural dynamics of pearl mussel host fish populations (removal of a maximum of nine barriers and adaptation of nine channels in the river); Improved connectivity of desman populations; Improved conservation status of the freshwater pearl mussel and Pyrenean desman; Improved conservation status of the river ecosystem and of other endangered habitats and species (Narcisus ciclamineus, Chioglossa lusitánica, Ch. arcasii, S. salar); Reinforcement of the pearl mussel population in areas where stocks are low, and reintroduction in other parts of the basin; Elaboration of environmental guidelines for watercourse management; Introduction of best practices and methodologies on the Ulla river basin farms; and The establishment of monitoring systems for the freshwater pearl mussel and Pyrenean desman populations and habitats.