As part of our community meetup in Eastern Bulgaria, we decided to tackle the at the time worst rated site: Srebarna. Srebarna is meant to represent the ecosystem of a contributary lake to the Danube. The Bulgarians also argue that it's a good birding site. When we came, though, birds were in as short supply as were other visitors or tour guides for that matter.
Peter was so kind to prepare some material to provide context. But without birds present it didn't help much that day. Indeed, Peter was adamant that Srebarna is not a very unique birding site simply on account of the limited diversity of the bird populations.
My personal impression was fairly underwhelming and I can see the following reasons:
Size: It's a fairly small national park.
No wow factor: The site doesn't have anything outstanding, e.g. a unique species or a great scenery.
Accessibility: There are very few trails and it's really hard to explore the site.
Upkeep: The site is really in bad shape. Trails are overgrown and several installations have fallen into disrepair. See Els' pictures.
To me the accessbility point is the key short coming of the site. You can't even get down to the lake proper. I did expect some learning trails taking you into the different parts of the ecosystem with some explanation boards: "This is a world heritage site and this is our claim to fame!" But no. For birding some dedicated platforms would have helped. If the Bulgarians need any ideas, Donana NP and Everglades NP could serve as templates.
On a certain level I can see that OUV should not be tied to questions as upkeep or accessibility. But it's really hard to appreciate or even just to identify it without. The end result is that Srebarna remains one of our lowest rated sites and deservedly so.
PS: The next day Philipp and I made good use of Peter's presentation. The diversity in the Danube Delta is immense and it was kind of hard to spot all the birds; there were just too many of them around. So if you are in the area and interested in wildlife, go to the Danube Delta.