Lacul Roșu (Romanian: Lacul Roșu, Hungarian: Gyilkos-tó – "Killer Lake") is the largest barrier lake, in the Eastern Carpathians chain in Harghita County, Romania. The name of "Lacul Roșu" comes from the reddish alluvia deposited in the lake by the Red Creek. The lake falls within the jurisdiction of the municipality of Gheorgheni.
It was formed in 1837, after a landslide blocked the Bicaz Valley. It is about 93 m deep and covers about 12.01 hectares.
