Osadnik Gajówka, Industrial water reservoir in Przykona Municipality, Poland.

Osadnik Gajówka is a constructed water basin in Przykona Municipality, Poland, born from an old coal mining site. The turquoise surface covers roughly 100 hectares (247 acres) and sits surrounded by sharp banks built from piled waste material left after extraction ended.

Osadnik Gajówka occupies part of the former open-pit lignite mine of KWB Adamów in Gmina Przykona. The basin was filled with water and is used by the Adamów Power Plant as a dump for ash and slag, transported here as pulp. The stored waste forms a cemented rock layer about 40 metres thick.

Locals call the reservoir Lazurowe Jezioro, the Azure Lake, after its turquoise surface. The northern viewpoint by the local road is the sanctioned place to take in the panorama; walking the shore itself is banned because the ground is marshy and the water strongly alkaline. The Panorama cycling route passes here, with information board number 13 describing the site.

A viewpoint at 115 m above sea level sits in the northern part of the basin, by the local road, and looks out over the water. Walking along the shore is banned: the ground is unstable and marshy, and the fire brigade has twice rescued people trapped there. The Panorama cycling route passes the site, with information board number 13 describing the reservoir.

The water reaches a pH near 12, making it strongly alkaline and causing cemented layers to form from old power station residue below. These hardened deposits stretch down around 40 meters (131 feet) and seal the bottom like a solid plate, fixing the waste material in place for decades.