Lewis & Short

Lĕmannus, i, m. (with or without lacus), the Lake of Geneva.
Without lacus: deseruere cavo tentoria fixa Lemanno, Luc. 1, 396; cf. Plin. 2, 103, 106, § 224.
With lacus: Rhodanus, Lemanno lacu acceptus tenet impetum, Mel. 2, 5, 5; 2, 5, 1; Plin. 3, 4, 5, § 33; Luc. 1, 396; Mart. Cap. 6, § 635.