The Seddinsee is a lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 situated in the south-eastern outskirts of Berlin

Berlin

Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

, the capital city of Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. The lake is aligned south-west to north-east, with its south-western end adjacent to the Berlin suburb of Schmöckwitz

Schmöckwitz

Schmöckwitz is a German locality within the Berlin borough of Treptow-Köpenick. Until 2001 it was part of the former borough of Köpenick.-History:The locality was founded in 1375 with the name of Smekewitz...

. Here the Seddinsee meets the Zeuthener See

Zeuthener See

The Zeuthener See is a lake situated to the south-east of Berlin, the capital city of Germany, in the states of Berlin and Brandenburg. At an elevation of , its surface area is .-Overview:...

 and Langer See

Langer See

The Langer See is a lake situated in the south-eastern outskirts of Berlin, the capital city of Germany. The lake is aligned south-east to north-west and forms part of the course of the River Dahme...

, two lakes which form part of the course of the River Dahme.

The Seddinsee is navigable. Besides its natural connection to the River Dahme, the Oder-Spree Canal enters the lake on its eastern shore, whilst the Gosen Canal links the lake's northern end to the Dämeritzsee

Dämeritzsee

The Dämeritzsee is a lake located in Brandenburg and Berlin, Germany. At an elevation of , its surface area is . It is located partly in the municipality of Erkner and part in Rahnsdorf, a Berliner locality in Treptow-Köpenick district....

. Besides seeing considerable sightseeing and leisure traffic, the lake also forms a link in several commercial navigation routes, including the route from Berlin to Poland

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

via the River Dahme and the Oder-Spree Canal.