Area of Kirkilai village, Biržai District Municipality
Biržai District
System of karst lakes
56.24700, 24.69000
1-2 hours
summer, when the pontoon path and tower are easiest to combine
Kirkilai lake system, Ilgasis, Upėgalis, Sinkhole Lake Nature Trail
A karst lake system near Kirkilai
Kirkilai Karst Lakes are one of the clearest places in the Biržai region where karst is visible not as one pit but as a whole landscape of water-filled sinkholes. Lakes, narrow necks, peninsulas, islands, and bays form a mosaic best understood by walking the trail and climbing the observation tower.
VLE describes the Kirkilai lake system as more than 70 karst lakes with a total area of 5.9 ha. This is not a simple recreational pond; it is an open-air lesson in the hydrogeology of northern Lithuania's karst region.
How the lakes formed
The origin of the lakes is linked with the dissolution of gypsum-rich layers of the Late Devonian Tatula Formation. When underground cavities form, Quaternary sediments above them collapse, and some sinkholes fill with water.
The largest lake is called Kirkilai, Ilgasis, or Upėgalis. It covers about 3.9 ha and formed when more than 30 water-filled sinkholes joined, which explains its winding shoreline and unusual form.
Water, colour, and living nature
Kirkilai water has unusual hydrochemical conditions: it contains many calcium sulphate ions, and layering by temperature and oxygen creates conditions for sulphur bacteria. Their purple accumulations can sometimes be seen with the naked eye.
Sources mention 46 zooplankton species and Natura 2000 status. The lakes are therefore valuable not only as a beautiful view from the tower but also as a sensitive ecosystem where visitors should stay on paths.
Pontoon trail and tower
The most convenient visit combines the Sinkhole Lake Nature Trail, pontoon bridges, and Kirkilai Observation Tower. From the boardwalks you see water and shoreline details; from the tower the sinkhole pattern becomes clearer.
Official descriptions mention asphalt, pontoon bridges, and forest paths. A stroller can be pushed on parts of the pontoon bridges, but transitions may be steep, so judge the route by real on-site conditions.
How to visit responsibly
In karst terrain, do not look for shortcuts across wet or uneven ground. Stay on trails, do not enter water-filled sinkholes, and do not damage the banks.
A Biržai karst route can also include Cow Cave, Likėnai Park and Smardonė Spring, or Biržai Castle. Then Kirkilai becomes part of a wider geological and cultural day, not just one photograph.
