The Södertälje Canal is a canal

Canal

Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...

 connecting the lake Mälaren

Mälaren

Lake Mälaren is the third-largest lake in Sweden, after Lakes Vänern and Vättern. Its area is 1,140 km² and its greatest depth is 64 m. Mälaren spans 120 kilometers from east to west...

 with the Baltic Sea

Baltic Sea

The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

, at the city of Södertälje

Södertälje

Södertälje is a city and the seat of Södertälje Municipality, Stockholm County, Sweden with 86,069 inhabitants in 2010.The industrial city, about south of Stockholm, is the home to truck maker Scania AB and a top 10 pharmaceutical company AstraZeneca....

. It is 5,2 km long, and it has one lock

Lock (water transport)

A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is...

. The size of this lock is the largest in Scandinavia by allowed ship size. The lock is 135 m long and 17 m wide. The water level difference between Mälaren and the Baltic Sea is not large, on average 0,6 m (2 ft). This is the main shipping route into the lake Mälaren.

History

In the Viking age the passage was navigable by boats, but the Post-glacial rebound

Post-glacial rebound

Post-glacial rebound is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy...

made it unusable. In the year 1819 a lock was finished, so boats could use the canal. In 1924 a much larger lock (remains in use today) was built and the canal was widened and deepened.