The 15,600 square kilometres (6,000 sq mi) reserve comprises the islands of Saaremaa, Hiiumaa, Vormsi and Muhu, as well as numerous islets and marine parts.

[1] The archipelago represents the ecosystems that have been formed on the coastal formations of different developmental phases of the Baltic Sea in the last ten thousand years.

The distinctive features and diversity of nature in the West Estonian islands is mainly influenced by the geographical position, young age of the area, lime-richness of soils and centuries of human activity.

Terrestrial habitats contain pine forests, mixed spruce and deciduous woodlands, juniper and coastal meadows, swamps and peat bogs.

[1] Valuable ecosystems consist of the shallows of the Baltic sea, islets, lagoons, grasslands (coastal, alvar, alluvial or marshy), woodlands and wooded meadows.