The Red Lake is one of the most beautiful and the most monumental lake of the Seklerland. About its formation there are several legends sprung from the people. Orbán Balázs, who during his travellings wrote legends about Seklerland, doesn't mention myths about the Red Lake. Urmánczy Nándor wrote for the first time in his itineraries about the legend, in which he memoralises a story told by an old sekler man. According to the legend a robber, who stayed in the cave of Suhardul Mare, had stolen from a fair in Ditrău and dragged along the beautiful Ferenc Anikó. The girl cried and implored the help of the cave ghost, when the walls of the cave opened and she escaped. When the robber came around, he banged the cliff with his bludgeon so strongly that the mountain collapsed and closed the valley burying under itself the robber. In the course of the years several variants of the legend appeared. The popular belief connects the "killing" and the "red " adjectives with the legend, whereas the collapsing mountain buried under itself the grazing herd together with its shepherd, the blood oozed up and painted the lake water red for a long time.
Despite the fact that the Red Lake is a relatively young formation, the date and conditions of its formation are debated. At the time of its formation there weren't any commercial routes in the surroundings, it was an economically idle and difficult of access region. Herbich F., the famous geologist of Seklerland, considers the year of 1838 as the formation date of the Red Lake. Argues in the favour of this year the earthquake from January 1838, which repeated in February and could have set off the landslide. An other date would be 1837, when wild tempest and and heavy rain took place. About this period wrote Ditrói Puskás F. in his work entitled "History of Borsec". "...at this time collapsed the two Bicaz mountains soaked by a huge mass of water, owing to which the brook flowing there got blocked up, forming the Red Lake..."
The formation and the slip of the conglomerated mass of debris at the foot of the Ucigașul mountain can be divided into three phases. In the first phase the basic debris has been conglomerated, which happened in the last stage of the periglacial period. In the second phase the slow weathering of the lower debris took place, finally the soaking of the debris, which set up the slide of the clayish stratum and led to the closing of the valley. We can see even today that headland, which closed the valley in its full width and now leans against the southeastern side of the Suhardul Mare.
The lake is bordered in the north by the Suhardul Mare and Suhardul Mic, in the southwest by the Calului mountain, in the northwest by the Licoș and the Mic mountains, in the northeast by the Csiki-bükk, in the east by the Ucigașul mountain. The Red Lake is supplied by four constant and twelve periodical brooks, among which the most important are the Oii(Hăghimaș), Roșu, Licoș and Suhard.
The original hungarian name of the lake was the Red Lake aswell, and the writers in the region used this name until 1864. On his presentation upon the assembly of the Transylvanian Museum Society, Orbán Balázs mentions as Killer Lake and makes it public. It got its present hungarian name probably from the Ucigasul mountain (means Killer's mountain), which is much more older naming than the formation of the lake, as the documents mentioned it even in 1773 as the Lazar Counts' property; it was called "the mountain named killer".