Lake Of Geneva, or Lake Leman (anc. Lacus Lemanus), the largest lake of Switzerland, extending in the form of a crescent, with its horns toward the south, between France, on the south, and the cantons of Geneva, Vaud, and Valais. Its N. bank forms an arc about 53 m. long, exclusive of the sinuosities; along its S. shore it measures 46 m.; and its breadth varies from 8 or 9 m. in the middle to 4 m. near the E. and 1 m. at the W. extremity; area, about 240 sq. m. Its greatest depth, which is on a line between Evian and Ouchy, is about 1,000 ft.; its average depth is 400 ft. Its elevation above the sea is about 1,230 ft., but in summer, when the Alpine snows melt, it sometimes rises 6 or 8 ft. higher. At other periods it presents in particular parts of the lake, most commonly near Geneva, the curious phenomenon of a rise and fall of from 2 to 5 ft. in the course of 25 minutes. These changes of level, called seiches, have never been fully accounted for, but are supposed to be owing to the unequal pressure of the atmosphere upon different parts of the surface. They are independent of the wind, and most frequent when the clouds are low and heavy. The lake is never frozen over, though ice forms in winter near its lower extremity.

Its waters are pure and bright blue, like those of the Mediterranean, the Rhone enters it at the E. end a dark muddy stream, and leaves it near Geneva perfectly pellucid and of the finest azure hue. The debris brought down by this stream are deposited around the upper end, and have made considerable encroachments upon its basin. Port Valais, 1- 1/2- m. inland, was formerly situated on the shore, and the waters are said to have extended as far as Bex, 12 m. up the Rhone. About 40 small streams discharge themselves into this lake. It has fewer fish than other Swiss lakes, but contains excellent trout, pike, carp, and perch, and a kind of salmon. Steamers ply daily between Geneva at the W. and Villeneuve at the E. end. The scenery is an unfailing theme of admiration to travellers. On the north are beautiful vine-covered hills dotted with villages; opposite, the abrupt cliffs of the Chablais rise 5,000 ft. above the lake. The majestic Alps are seen beyond them through the openings. On the east, between the lofty summits of the Dent de Morcles and the Dent du Midi, about 9,000 ft. high, a narrow pass opens into Valais, while at the W. end the lake narrows almost to a point, and terminates among the pleasant slopes on which stand the city and suburbs of Geneva. The lake is famous in literary history as the scene of the Nouvelle Hele'ise, and for the abode in its vicinity of many celebrated authors.