Location
Special Protection Area, which covers 33665.8 ha, stretches eastward from Katy Rybackie and the Nogat estuary up to the Russian border. It encompasses Polish part of Zalew together with a narrow fragment of Mierzeja Wislana coast and a belt of low shore which encircles the refuge from south.

Geology and Land Formation
Zalew Wislany was created 5 thousand years ago when Vistula sand bar cut it off from the Baltic Sea. Initially Zalew was connected with vast floodplains and marshes inside the estuary of Vistula river and had at least periodical connection with the Baltic sea. In 1497 a canal through Mierzeja Wislana was built near Pilawa (presently Baltijsk). From then on the lagoon has a constant contact with the Baltic. In 1960s the Straits of Baltijsk was expanded to the width of 400 m and the depth of 12 m which caused the increase of water exchange with the Baltic (increase of salinity, intensification of the water level fluctuation in Zalew). Polish part of Zalew Wislany has  the average depth of 2.3 m (maximal 4.6 m) but due to stormy winds the water level may change even by about 150 cm during 24 hours.

Ecosystem
Almost 90% of the area is occupied by the waters of Vistula Lagoon. The remaining part is land overgrown with alluvial forests in the west and peat bogs in the north. Rush vegetation forming vast belts up to 1 km wide grow by on the water shores. The most important bird breeding areas are located in the Pasleka river estuary, in south-west coastal zone and in Zatoka Elblaska (the Elblag Bay). The following smaller rivers also have their estuaries in the area: Nogat, Elblag, Pasleka, Bauda.

Flora
Greater part of Zalew Wislany coast is overgrown by reed belt, up to a few hundred meters wide. Shallow bays in the western part of Zalew are rich with submerged and floating vegetation - green algae and pondweed meadows as well as vast lobes of yellow water-lily and white water-lily. On area of open waters of the reservoir there are almost no vascular plants.

Fauna
Occurrence of 27 species of birds specified in 1 Appendix of the Birds Directive and at least 9 from the Polish Red Data Book of Animals has been recorded within the area of Zalew Wislany. It is the largest Polish refuge of cormorant. Numerous flock of this bird hatches in a forest near Katy Rybackie. Cormorants which nest here are about half of the country's population. Another numerous species in the area is a Black-headed Gull. The refuge is also a feeding ground for black heron flying over here in flocks.

During migrations many species of ducks and geese can be spotted on the waters of Vistula Lagoon, among them: Canada goose, Taiga bean goose, greylag goose, common goldeneye, common merganser, greater scaup, Eurasian wigeon and northern pintail.

Zalew Wislany is also rich with species of sea fish, among them: trout, herring, bulltrout, bream, perch, roach, pikeperch and asp. Species of water animals which come from foreign geographic regions (including South-American) have settled in the waters of Zalew Wislany, for example: Estaurine mud-crab, spiny-cheek crayfish and a few species of freshwater shrimp and recently arrived round goby - a fish which comes from the Black Sea and the Caspian Sea.

Threats

• setting traps and fishing nets, in which birds die, excessive fishing;
• wastewater damp;
• inflow of fertilizers to the waters of Zalew;
• abandonment of pasturage;
• overgrowing of the area in result of eutrophication;
• scaring off animals, destroying vegetation, pouching;
• development of touristic objects, building artificial beaches;
• deepening of fairways and strengthening of shores.

Protection of Nature
"Zalew Wislany" Special Protection Area is located within two landscape parks: Wysoczyzna Elblaska (13460.0 ha) and Mierzeja Wislana (4410.0 ha) and encompasses two nature reserves: Ujscie Nogatu (356.7 ha) and Zatoka Elblaska (420.0 ha).