| Lake Rândunica | |
| Other Name: | Lacul Sf. Ioan |
| Location: | Ocna Sibiului, Sibiu County, Transylvania, Romania |
| Coordinates: | 45.8731°N 24.0665°W |
| Type: | Salt lake |
| Area: | 2149m2 |
| Max-Depth: | 46.54m (152.69feet) |
| Salinity: | 120 g/l |
| Pushpin Map: | Romania |
| Pushpin Map Alt: | Location of the lake in Romania. |
Lake Rândunica (Romanian; Moldavian; Moldovan: Lacul Rândunica, also called Lacul Sf. Ioan) is a natural salt lake in the town of Ocna Sibiului, Sibiu County, Transylvania, Romania. It is one of the many lakes of the Ocna Sibiului mine, a large salt mine which has one of the largest salt reserves in Romania.
Lacul Rândunica means the swallow lake.[1]
The origin of this lake is the abandonment of the "Nepomuceni Johann Grube" salt mine. The salt mine was exploited between 1722-1877 using the bell system with two wells up to the depth of .