According to the legend, emperor Lê Lợi was boating on the lake when a Golden Turtle God (Kim Qui) surfaced and asked for his magic sword, Heaven's Will. Lợi concluded that Kim Qui had come to reclaim the sword that its master, a local God, the Dragon King (Vietnamese: Long Vương) had given Lợi some time earlier, during his revolt against the Chinese Ming Dynasty. Lợi renamed the lake to commemorate this event, it was formerly known as Luc Thuy meaning "Green Water"). The Turtle Tower (Thap Rùa) standing on a small island near the centre of lake is linked to the legend.