The site consists of the three largest islands in Usma lake, covering about a quarter of its area. Moricsala island (83 ha; protected since 1912) is covered by an old-growth deciduous forest, Viskuzu island (309 ha) holds mostly coniferous forest. Part of the IBA was first listed in 1994 , now it qualifies under the IBA C criteria. Fully protected: there is a 97.2% overlap with Moricsala nature reserve and the newly designated Viskuzu island restricted nature reserve, both candidate SPAs. The gap between IBA and pSPA boundaries is due to differences in methods of boundary setting.