The site encompasses the nutrient-rich lake and adjoining wet forest and open areas with many swamps. Most of the previously pastured areas are no longer used, and have reverted to swamps occupied by young alder Alnus wood or sedge meadows. Open water is not extensive, and the greater part of the lake is covered by reedbeds Phragmites. There are seven islands (all forested). The Owinka river (tributary of the £yna) rises from the lake.
Breeding species of global conservation concern that do not meet IBA criteria: Haliaeetus albicilla (one pair), Crex crex (four pairs). A total of 126 species have been recorded.
Pressure/threats to key biodiversity
Following drainage operations in 1970 and intensive abstraction of water from the Owinka river outside the Nature Reserve, the lake-level fell by c.1 m. This caused extensive vegetational changes, and reduced bird numbers. To raise the water-level once more, a dam was built on the Owinka river in 1993. Hunting is unsustainable, and tourism/recreation causes disturbance to birds. There is a proposal to expand the Nature Reserve boundary, based on studies in 1996.
National Partial International Partial1,007 ha of IBA covered by Nature Reserve (Jezioro Siedmiu Wysp [Bird Reserve], 1,007 ha). 1,007 ha of IBA covered by Ramsar Site (Jezioro Siedmiu Wysp, 1,007 ha).