Correcting a badly made lake

Hello all,

I would like to correct a badly built lake. The polygon folds into itself :

I would like to correct it in JOSM but as you would agree, I do not want to draw all the nodes myself. I would like to reshape/reuse them so that the resulting multipolygon is fine. I have been looking for hours in the wiki and the forum and in JOSM but as a beginner, I still cannot figure out how.

Could someone please point me to the right direction?

Firstly, the ways around the lake should not be tagged as natural=coastline. That coastline tag is for mapping coasts next to the sea, not inland lakes.
It should be tagged as natural=water and/or landuse=reservoir

Second, the way around the lake should be a single closed way (ie an area) around the lake. It is currently split up into 4 separate ways. To join these ways, select several of them in JOSM (use shift+click), then go to tools menu → combine way (or press C).

Note that a single way can have a maximum of 2000 nodes, so for larger lakes you may need to have several ways and a multipolygon relation. But that is not the case here, the lake is only made up of about 1000 nodes.


Your remarks were helpful. I was able to join the roads and set natural=water. Thanks a lot for your kindly help