Lakes of the Reserve are heavily overgrown and waterlogged. Almost half of Žuvintas lake’s water surface is covered by the aquatic vegetation, constituted of reeds, cat’s-tails, bulrushes. The common characteristic of this lake – floating “islands”, formed of interlaced rhizomes of Typha angustipholia, Phragmites australis, etc. macrophytes. The predominant aquatic plant species are composed of pondweeds, filamentous algae (Chara canescens, Chara baltica), water milfoils, spatterdocks, water lilies. Very important colonies and plots composed of Chara algae, which is the nutrition source for water birds. These Lakes are distinguished for their abundance of fishes, among others – pikes, perches, breams, and snappers. Several fish species, Common loach and Weather loach, are under the European protection.  Abundance and variety of water birds distinguished characteristic of Žuvintas Lake. Number of migratory geese reaches up to several thousands. Montagu’s Harrier, Marsh Harrier, Bitterns, Beared Reedlings (Tits), Little Crakes, March Crakes, Spotted Crakes nest in lakeside vegetation, Whistling thrushes- in scrubs. There can also be found Otters, Beevers and American Minks. The number of latter species has been regulated.