The Old Lake has a special value in maintaining ecological diversity of this region, this role is
outstandingly unique within a city. The extended site is one of the few major stopover sites for
migratory birds in Transdanubia (Hungary west of the River Danube). Thereby, it is essential to
maintain these migrants in the region. It is the only other site apart from lake Fertő where the
endangered Lesser White-fronted Goose annually occurs. For list of all internationally designated
bird species, see Criterion 2. It is also one of the three sites in Hungary where Senecio umbrosus
occurs, and the only site in northern Transdanubia for Ludwigia palustris.