Oostvaardersplassen, Netherlands

Oostvaardersplassen triggered one of Europe's most intense conservation ethics crises when 3,000 Heck cattle and Konik horses starved during the winter of 2017–18, sparking death threats against park managers and a national inquiry. The project allowed natural processes to run without intervention on 5,600 hectares of reclaimed polder, but 60% of the ungulates perished in that single season, leading to public outrage that forced a policy shift to managed culling. This disaster is more polarizing than #8 Tasmanian Devil Reintroduction, which at least operates within fenced safety zones. A subsequent ethics panel recommended mandatory feeding thresholds — a regulatory response that has tempered the project's wildness but not its legacy as a cautionary tale.