The lack of scale makes this a little tricky, but that said I think this may be a water shrew. There are two species in Germany, but I wouldn't be able to pin it down between them.
Do you have a more precise photo of tail & hind legs? At least it looks very much like a water shrew, and as the millers water shrew does not live in S-Holstein, it will be the "normal" water shrew.
