Ertso Lake is a karst lake in Java municipality, in the Kvirila River basin, on the Tskhinvali–Oni road 36 kilometers from Tskhinvali, 1,710 m above sea level. Surface area 0.31 km². Greatest depth 19 m, average depth 2.1 m. It occupies four karst funnels and is fed by rain and snowmelt. Its level is highest in May–June and lowest in August–September. It freezes in winter. The lake holds no fish.