Once abundant in the brooks of northern Germany, the industrialization and the cultivation of adjacent areas made the freshwater pearl mussel disappear. This species of mussels needs extremely clean and sediment free water to thrive and is used as a bioindicator for water quality.

Reinhard Altmüller, a former employee of department of nature conservation of Lower-Saxony, made it his life’s goal to bring back the mussels to his a creek near his home town. This endavour took him decades as the entry of fertilizers and sediments needs to be reduced along the whole creek, a task only possible in cooperation with local stakeholders and farmers.

Now, 40 years after he started working on the freshwater pearl mussel they are slowly making a comeback. This reportage for GEO follows him on his weekly trips along the brook.