Lacul Roşu or Ghilcoş (English: The Red Lake, Hungarian: Gyilkos-tó) is a natural dam lake and it belongs to a very picturesque natural reserve of complex (geological, botanical and landscape) importance. It is situated in the Eastern Carpathians, at 980 m altitude, near Bicaz Gorges, at approximately 26 km from Gheorgheni city (Harghita County). The lake has "L" form, its maximum depth is 10.5 m, has an area of 12.7 ha, and a 3090 m circumference. The name Red Lake comes from the reddish alluvia deposited in the lake by its main tributary (Red Creek).
The lake was formed recently, in the summer of 1837. Then, after some abundant rains, a great quantity of rocks and debris slided from the Northen side of the Stânca Ucigaşului (Killer's Rock), blocking the Bicăjel River. The water have accumulated and formed a natural storage lake. The unusual magic is amplified by a lot of trunks of the old fir trees, which come out from the water passing through the image of Little Suhard Mountain reflected in the lake mirror. Seen from the underwater view, with the diver's eye, the surprises of the lake are major: tree trunks are still vertical, in central areas the ground is horizontal because of vegetal clasts accumulated in huge quantity, the fauna is rich and friendly, everything excepting the last aspect inviting to forget the underwater environment and to belive in a legendary, maybe a rather melancholic forest. Seen with the paleo-botanist's eye, the lake has again surprises because the vegetal deposits and in situ trunks may reveal their history.
The local tradition keep a legend related to the lake origin:
Once lived in Lăzarea a very beautiful girl with the name Estera. One day she went to the fair in Gheorgheni, where she met a handsome and strong lad (he could fight with a bear). They felt in love immediately. The lad asked her to be his bride, but the wedding did not take place because the lad was taken to army. The girl waited for him. On the evenings, when she went for water to the spring, she sang so sadly that even the mountains were touched.
In a Sunday afternoon she was seen by a thief. The thief lifted her and run away as quickly as he could to Suhardul Mic, the rock with a thousand faces, were he lived. He promised to Estera gold and silver only to love him, but she refused. The thief lost his patience and forced her to marry him. She shouted to the mountains, begging for help. The rocks responded by thunders. A big rain started, whipping all in its way. The girl and the thief were buried under the rocks. After that, the waters were gathered here forming the lake Red Lake or The Killer.