Luossajärvi is a small 260-acre (1.1 km2) lake in Kiruna in northern Sweden beside Luossavaara.

The remaining portion of the lake has a chemical composition which shows the influence of mining activities.

The high sulfate concentrations indicate extensive weathering processes of mainly carbonate and sulphurous materials.

The spawning ground for the natural brown trout populations has disappeared due to mining.

However, other fish species have been introduced, including whitefish, grayling, char, rainbow trout and splake.