The Curonian Lagoon is a transnational lagoon shared between Lithuania and Russia Federation. It is a shallow waterbody with an average depth of 3.8 m. With a total area of ∼ 1,584 km², it is the largest coastal lagoon in Europe. The lagoon lies at the interface between the south-eastern Baltic Sea and the watershed of the Nemunas River. The Nemunas River is one of the largest river systems in the eastern part of the Baltic Sea and the largest river in Lithuania, which contributes the most in terms of water, sediments, and nutrients to the Curonian Lagoon. Concerning nutrient loads, it is one of the four most important rivers in the Baltic Sea region. The consequence is a heavily eutrophicated lagoon with frequent, potentially toxic, cyanobacteria blooms in late summer.

Nemunas delta is a managed Nature Reserve, Regional Park, Natura 2000 and a recognized RAMSAR site. The river delta comprised of marshes, raised bogs, ridge-pool complexes, flooded forests and meadows. The site supports a rich plant community with numerous endangered species. Located on the East Atlantic flyway, it is an internationally important breeding, wintering and passage site for thousands of waterbirds and migratory birds, many of which are threatened species. Over 60,000 migratory birds are ringed annually at the site. The management is performed through conservation, ecological protection, recreational, economic and residential. Human activities include conservation education, hay production, dairy farming, fishing, hunting, peat production extraction, recreation, and tourism. The site is visited by more than 100,000 visitors per year. 

One of the most prominent features of the Curonian Lagoon‘s surroundings is the Curonian Spit, a long, narrow sandbar that separates the lagoon from the Baltic Sea. The Spit stretches approximately 98 kilometers and is known for its impressive sand dunes, some of which reach heights of up to 60 meters. These dunes are constantly shaped by wind and weather, creating a dynamic and ever-changing landscape. The Curonian Spit is covered with diverse vegetation, including pine forests, meadows, and unique coastal plant species. The area is also home to the Dead Dunes (or Grey Dunes), which are large sand dunes devoid of vegetation, creating an otherworldly landscape. The Curonian Spit (governed by the Neringa municipality) is one of the most popular local and foreign tourist destinations in Lithuania and hosts 400,000 guests per year.