I'm sorry, I didn't notice that. Thanks for taking the time to improve the map.

When mapping a marina, you should draw an outline around not just the water basin, but also the facilities on land (like the toilets, front desk, etc.). Usually the whole grounds. So leisure=marina shouldn't share the same shape as natural=water. This used to be neglected, so you can often see examples where only the water is tagged with leisure=marina. Here in Terherne this happened too.

The wiki can help:

https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dmarina

Or in German if you like (the created_by tag of your changeset indicates you run JOSM in German):

https://wiki.openstreetmap.org/wiki/DE:Tag:leisure%3Dmarina