Background Although the Annex II freshwater mollusc Margaritifera margaritifera is colloquially named the freshwater pearl mussel, only one in 7 000 of these sensitive mussels produces tiny pearls. Some 30 000 of the species, 20% of the total population in Germany, live in streams in the project area, a species rich man-made landscape located at the border of Bavaria, Saxony and the Czech Republic. The streams are also home to another Annex II mussel, Unio crassus (common river mussel). Once sparsely populated and with little industry, the project area has seen increasing modernisation and urbanisation since emerging from the shadow of the “Iron Curtain”. For the highly sensitive molluscs, this has spelt danger: even mild contamination from pollutants and nutrients can lead to the absence of offspring and the death of older mussels. Discharges of polluted water, increased drainage of adjacent land into the streams (precipitating iron oxides) and cattle being driven through the streams have all contributed to a decline in population (the Unio crassus population in the project area was only 100 strong) and premature aging of surviving mussels. Objectives The project aimed to improve the habitat for the molluscs and the host fish (Salmo trutta fario, Phoxinus phoxinus) that their parasitic larvae, the small glochidia, depend upon during the reproductive cycle. Following improvements to the habitat, the aim would be to increase the mussel population in the project area. River restoration steps to be taken in the first phase of the project would include construction of silt traps, drainage openings, a ‘mussel ditch’ and fords for cattle. The most visible measure would be to free the last 400 metres of a stream from its drainage corset to let it meander. The second phase of the project would see the release of infected host fishes and juvenile mussels. The project would be evaluated through monitoring of sediment load, monitoring of mussel development and monitoring of fish-stock and young mussel development. A series of dissemination and public awareness actions was also planned. Results The project reached the main objective, the improvement of the habitat conditions for Margaritifera margaritifera and Unio crassus. Some 3.26 ha of land was purchased, eight silt traps were constructed, five drainage pipes opened and the sediment structure of the ditch foreseen as young mussel habitat was improved. In addition, three fords for cattle were built. The project succeeded in reducing the silt and flocculent ferric hydroxide load in the streams, and managed to improve the habitat conditions for host fishes. Young freshwater pearl mussels were released in five campaigns in the Südliche Regnitz and Zinnbach creeks and on two occasions in the Höllbach and Mähringsbach creeks. Some 342 000 Margaritifera margaritifera were released in total. In addition, autochthonous infection of Phoxinus phoxinus with young common river mussels was undertaken three times, a total of 115 000 Unio crassus being released. It could not be determined before the project end if the project was successful in the rejuvenation of the mussel populations, because during the first years of life mussels are too small to allow a meaningful population control. Results of the project were disseminated through a series of measures including information events for the local public, guided tours, workshops, leaflets, information boards and a travelling mussel exhibition. Further information on the project can be found in the project's layman report (see "Read more" section).