I just found a huge dam missing in Germany. This surprised me as I thought Germany was more or less “complete”. It had been an untagged line (osm.org/#map=17/51.11237/7.89440) until I added a name and the tag “waterway = dam” to it today.

In its immediate vicinity there are things to be found like

• a vending machine for excrement bags node/681507482
• 2 Webcams node/2975537573, node/2975537574
• a bench node/2954092511

but nobody noticed the dam wasn’t on the map.