Kozłowa Góra Reservoir (Lake Świerklaniec)

Kozłowa Góra Reservoir, also called Lake Świerklaniec, was built in the 1930s as… an anti-tank obstacle. In the event of war it was meant to flood the Brynica valley in front of the fortifications of the Silesia Fortified Area. Today it is a drinking-water reservoir for part of the Upper Silesian conurbation and one of the most important bird refuges on its northern edge, with more than 200 species recorded nearby.

History: water as a line of defence

Construction began in 1935 and was completed around the turn of 1938 and 1939. The designer and chief site engineer was Jan Stonawski. In an emergency, the stored water was to flood about 600 ha of the valley and hamper the movement of troops and armour. Bunkers, anti-tank barriers and firing positions were built around it, and some of them survive. In September 1939, however, the reservoir was not used as its designers intended.

In 1948–1951 the lake was adapted to supply the regional water network. The Kozłowa Góra water treatment plant of the Upper Silesian Waterworks (GPW) operates by the dam, and access to parts of the shore is restricted to protect the water intake.

The reservoir in numbers

• Area – about 5.5 km² at normal water level, with a capacity of 13.05 million m³.
• Size – about 3.6 km long and 1.5 km wide on average, with a shoreline of about 12.5 km.
• Depth – on average only about 2.4 m, at most around 4.5 m; it is a shallow lowland lake that warms quickly and is easily whipped up by the wind.
• Dam – an earth dam about 6 m high closes the reservoir to the south, with embankments running along the west side.

Nature: birds of the backwater zone

The most valuable part is the north of the reservoir, where the Brynica flows in, with reed beds, rushes and wet meadows. Some sources list 202 bird species recorded around the lake, 78 of them breeding, while others give at least 246 species. Breeding birds include the bittern, little bittern, spotted crake, marsh harrier, kingfisher, whiskered tern and black-necked grebe, whose colonies have reached about 90 nests. According to Birdingplaces, cranes and white-tailed eagles also breed in the area. Beavers and otters are seen by the water.

Interesting facts

Before the First World War the border between the German Empire and the Russian Empire ran along the Brynica valley, and traces of it can still be found nearby. The reservoir's official name comes from Kozłowa Góra, now a district of Piekary Śląskie. Locals also used the unofficial nicknames "Dioblina" or "Diablina". During construction some tree stumps and roots were left on the bottom, and for decades they affected fish habitats and angling.

Tripto tip

The reservoir lies about 20 km north of Katowice. It is best explored on foot or by bike, for example along the embankments, and combined with the neighbouring park in Świerklaniec (about 154 ha, with about 20 historic buildings including the Cavalier's Palace and the Donnersmarck mausoleum). For birds, come early in the morning in spring or autumn and bring binoculars. There is no designated bathing area – this is a drinking-water reservoir – and fishing is allowed only where and as permitted by the operator. Allow 2–3 hours for a walk with some birdwatching.