Thanks for doing that. As a newcomer to OSM editing, I found the idea daunting. JOSM is not easy but when I had a go elsewhere I found it could do things that the in browser editor could not. Today I have had a battle getting it to open from Firefox to look at how you have done it - finally sorted. Ther has just been a document released by Banks for the next phase, which is pushing for even more development than the outline planning agreed.
http://www.banksgroup.co.uk/wp-content/uploads/2016/12/Community-Update-Newsletter-December-2016.pdf

So far as I know, it is not actually a nature reserve, just a pond that is used for bridwatching.

Agreed. I've not visited for a couple of years, but the Durham Bird Club magazine had an article about open days last month at the hide, which is what triggered adding it.

The noise from the builders about a hundred yards away from me belies that!
I'll try to get time to review how you have done it and make some changes. At present I could probably onlly walk the perimeter fence of the latest area to mark the area as construction.