It's really surprising for me that Common Scoters are this far inland, on that small pond, close to a city.
The sea is at least 350 km away and in between is a typical German landscape with lots of forests and farmland, with only a few lakes.
Smews can appear on smaller waters but in the Netherlands they stay close to the coast, large rivers and lakes. Common Scoters are rare on fresh water here.
For english speakers, in German a lake is called ''See'' '(pronounced as 'zay') and the sea is called ''Meer'.
For Dutch speakers it's even more confusing, a lake is for us ''meer'' and the sea is ''zee'' (pronounced as 'zay'). In German ''meer'' is ''See'' and ''zee'' is ''Meer''
So Olbersdorfer See sounds huge to us but is in fact just a lake.