Lake Gyilkos (old name: Red Lake) is a natural dam in the Hagymás Mountains, in the Eastern Carpathians, in the northeastern part of Hargita County. It was created in 1837 as a result of debris sliding down from a nearby mountain.
According to data recorded in the 1960s, the riverbed is filled with 4.88 cm of sediment every year, and the lake will disappear completely by 2080 without human intervention. They tried to prevent the filling with two sediment catchment dams nearby.