The Lakes, Copenhagen

The Lakes () in Copenhagen, Denmark are a row of three rectangular lakes curving around the western margin of the City Centre, forming one of the oldest and most distinctive features of the city's topography. The paths around them are popular with strollers, bikers and runners.
History.
Originally the area, which the lakes now form, was one long stream. It had an arch shape and was just outside the city levees. In the early Middle Ages, a need of water for watermills was determined. As a result of this a dam was built and the Peblinge Sø was created.
As a result of a siege of Copenhagen in 1523, it was decided to expand the entrenchments in order to improve the fortifications of the city. The levee at Peblinge Sø was expanded and another was created, which resulted in the creation of Sortedams Sø. In the beginning of the 16th century, Sankt Jørgens Sø was created, by further damming. This made it possible to flood the banks and lakes in case of an attack.
Peblinge Sø and Sortedams Sø also served as reservoirs for the city, and in the period 1705–1727 they were cleaned and dug deeper. The edges were also straightened, giving them their current shape. In the middle of the 18th century they were discontinued as a source of drinking water, due to poor water quality. Sankt Jørgens Sø was to be used instead and it was cleaned and straightened in a similar manner as had the two other lakes 120 years earlier. Until the end of World War II, it played a central role in as a reservoir in Copenhagen and as a backup reservoir until 1959.
The first Fredensbro (bridge) was built across Sortedams Sø in 1878 as a small wooden bridge. The current Fredensbro is a wide levee, that separates the two basins. It was created in 1976–1977.
The vertical slopes of Peblinge Sø and Sortedams Sø were made in 1929, where the pathways surrounding the lakes also were made. In the 60's it was suggested a four lane city ring (named "Søringen") be constructed, but the project was disbanded and the lakes were granted the a status of a protected area in 1966.
Fugleøen (the Bird Island) is located within the northern basin of Sortedams Sø. It was raised to fame in 1967, when it was "liberated" by a group of activists, who declared it an independent state, separate from Denmark.
There are plans to create a park around Sankt Jørgens Sø, with the dual use of acting as a detention basin for cloudburst flood waters. Likely as a consequence of Global Warming, cloudbusts have become much more common in Denmark, making the sewerage pipes designed for the old weather patterns insufficient; using Sankt Jørgens Sø as a detention basin is just one of many such projects in Copenhagen. The municipality of Copenhagen together with Nordic Innovation, an organisation under Nordic Council of Ministers, is launching an extensive climate adaptation and urban space initiative with objectives such as redirecting rainwater from cloudbursts, purifying the water running into the Peblinge City Lake, and creating new, attractive and more liveable urban spaces. Ramboll is Technical Lead this project team which is led by the design studio SLA.
Geography.
The landmark consist of three artificial lakes, which are divided into five basins:
Water.
The lakes inlet is through piped streams ("Grøndalsåen", "Lygteåen" and "Ladegårdsåen"). These streams jointly provide water from the wet-area "Utterslev Mose", the lake "Emdrup Sø" and to a lesser degree the lake "Damhussøen". "Ladegårdsåen" was converted from an open stream to a piped stream in 1925 and is located below the streets "Ågade" and "Åboulevarden". It provides water for Peblinge Sø and has its endpoint near the pavilion "Søpavillonen" (). From the lakes the water is streamed further on, with an endpoint at the north end of Sortedams Sø, to the lakes in Østre Anlæg, the Fredrikshavn Entrenchment and Øresund. The water has an average time in the lakes of approximately 1 year.
The water in Utterslev Mose and Emdrup Sø is very high in nutrients. As a result of this, large quantities of algae formed in the lakes and the water became rather unclear as well as hindering animal and plant life. In 1999 the municipality of Copenhagen erected a water treatment plant by Emdrup Sø, to clean the water that was being led to the lakes. This allowed for the re-creation of the water environment. Currently the water is much more clear and animal and plant life are present.
Use.
The lakes primarily serve as a recreational area and the paths surrounding them are popular for strolls and a favoured running route. The total distance around the lakes is 6.4 km.
Sankt Jørgens Sø has a depth of 4–5 metres with sloped sides. The other lakes have a depth of 2.5 metres, with hard vertical edges (made of granite). In Sortedams Sø, two artificial islands has been created. They are named "Fiskeøen" () and "Fugleøen" () and both serve as sanctuary for birds.