The site is a large complex of lakes, forests, and transition and bog mires. The core of the IBA is Osveia Lake which defines much of the hydrology and climate of northern Belarus.
A total of 164 breeding bird species have been recorded, including 36 species listed in the National Red Data Book. Osveia Lake is one of the largest breeding and post-breeding grounds in Belarus for numerous huntable waterbird species: Mallard Anas platyrhynchos, Pochard Aythya ferina, and Coot Fulica atra. The Lake and the surrounding areas have a high value for large concentrations of waterbirds during spring and autumn migration.
Non-bird biodiversity: A total of 16 National Red Data Book plant species have been recorded. Some rare plants include hybrids of Black Alder and Grey Alder (Alnus glutinosa and A. incana), tall-stalk forms of Betula pendula var. carelica, a large population of Yellow Pondlily Nuphar pumila, as well as a rare insectivorous plant Waterwheel Aldrovanda vesiculosa.Four mammal species found on the site are listed in the National Red Data Book of Belarus.
BirdLife International (2021) Important Bird Areas factsheet: Asvieja. Downloaded from http://www.birdlife.org on 27/01/2021.