Someone gave the Ruhr river (a linear feature) a key-value-pair called "landuse=basin". The result was that the whole town of Neheim (now Arnsberg) was afloat. Changed that.

By the way I noticed that the Ruhr is intermitted between somewhere north of Neheim and Wickede as well as between Wickede and Menden. Potlatch does not know of any deleted ways, so it seems that they have never existed. If anybody knows any (copyright-free) sources for the Ruhr river, feel free to complete its run.