Located in Arjeplog Municipality in the province of Swedish Lapland, administratively known as Norrbotten County, it is the deepest lake in Sweden at 221 metres (725 ft).

Due to the cold subarctic climate of the area, it always freezes over for several months of the year in spite of its depth.

The lake then extends 70 km (43 mi) northwest up to the town of Jäckvik, containing about 400 islets, many of which have distinguishable flora and fauna.

Research on the ecosystems comparing the larger islands with smaller islets in Hornavan and Uddjaur are popular due to their unpolluted environment, and have yielded rewarding results[clarification needed].

In June 2005 an international study was published in Nature entitled Effects of species and functional group loss on island ecosystem properties.