The fauna of water bodies located in Polistovsky Reserve is not rich in composition, reflecting primarily the chemical composition of water (low salinity, high acidity, high contents of humic substances), adversely affecting many species and groups of aquatic organisms.
The lakes of Polistovsky Reserve are inhabited by two species of fish - Perch and Pike; they are highly resistant to acid effects. Dip marsh ponds are generally more elongated. Color Perch is very dark, almost black, with pale transverse stripes on the sides of the body. Fins are brownish-orange. Pike also features a darker, golden color, and a bright yellow belly. The zooplankton composition of lakes of Polistovsky Reserve (Dolgoye, Krugloye, Russkoye and Mezhnitskoe) includes 40 species of organisms, of which 5 - Rotifers, 7 - Copepods and 29 - Cladocera Crustaceans. The basis of diversity includes predominantly Benthic Cladocera found in single specimen.
The zooplankton composition of the studied rivers in Polistovsky Reserve features 67 species of zooplankton (19 - Rotifers, 10 - Cladocera and 38 - Copepods). The species composition of aquatic macroinvertebrates of Polistovsky Reserve is not evidently enough studied to date. In lake Kruglolye researchers registered 18 species consisting of insect larvae (mainly Dragonflies, Caddis Flies, Chironomids), as well as adult beetles. It is noteworthy that researches have found here Dytiscus latisimus and a kind of Chironomids species, that were not previously registered in Pskov region, Endochironomus donatoris. Among mass type species in lakes and wetland ponds of Polistovsky Reserve one can note ephemera Leptophlebia vespertina, adapted to living in waters with low pH; a
mass departure of this type usually occurs in the second half of May. The avifauna of internal marsh ponds of Polistovsky Reserve is relatively undifferentiated. Every year one can observer here European Teal Mallard, Gadwall, Tufted Duck. Black-throated Diver - about 5 pairs - is regularly nesting. Along the banks there are nests of Fiddler, Wood Sandpiper; Whooper Swan and Wigeon can be noted on the flight; sometimes one can observe Great Crested Grebe and Common Merganser. Flocks of geese, mostly White-fronted, can stop for the night. For feeding purposes, lakes are visited by gray gulls nesting on the ridge-hollow complex of nearby bogs; once one Herring Gull was observed. Researchers repeatedly noted hunting osprey, although its breeding in the Reserve was not significantly determined.
In reservoirs of Polistovsky Reserve and its buffer zone scientists found Ordinary Newt, Brown Frog, Moor Frog and Edible Frog. Common Toad is sufficiently numerous; Spade-footed Toad is rare. Among common species of the theriofauna one can point out European Beaver, River Otter and American Mink. Among domesticated species we can observer Muskrat and Raccoon Dog often hunting in the coastal zone.