Lake Hornborga, Bird sanctuary in Västergötland, Sweden.

Lake Hornborga is a lake in Västergötland, about 15 km southeast of Skara, with a surface area of 28 square kilometres; the Natura 2000 area around it covers 40 square kilometres. Its outlet flows into the river Flian, and the water there does not freeze in winter. The lake is shallow and bordered by reeds and wet meadows.

Lake Hornborga formed about 10,000 years ago as the ice sheet melted, and Stone Age settlements and dog burials from around 8000 BC have been found nearby. The first lowering of the water level came in 1802 to create pasture during famine, followed by four more, the largest begun in 1841 and 1872 and the last in 1933, cutting the surface from 28 to under 4 square kilometres. Reeds replaced the intended farmland, and after a 1965 government investigation the level was raised by an average of 0.9 metres between 1992 and 1995, with 11 km of canals filled in and 1,200 hectares of reed and 800 hectares of trees cleared.

The lake's name, recorded since the 18th century, comes from Hornborga parish; its older name, Lonen (originally Lodhne, meaning 'hairy' or 'overgrown with water plants'), survives in local records. The spring crane gathering is watched from sites such as the Naturum at Broddetorp and the outlet where the water flows into the Flian river.

The Naturum visitor centre at Broddetorp, on the lake's eastern side near the village, has displays on the lake's nature. Birdwatchers head to the outflow where the water runs into the Flian river; it never freezes there, so birds can be watched year-round. The Ore backar trail follows part of the shoreline.

The record count at Lake Hornborga was 27,300 cranes on 3 April 2019, surpassing the previous record of 26,500 from 3 April 2012. The birds rest here in spring before continuing to breeding grounds in central Sweden and Norway, and again in autumn before flying south to winter in Spain.