The detritus of the Rhône has filled up this portion of the bed of the lake, and it appears that within the historical period the waters extended about 2 km (1.2 mi) beyond the present eastern margin of the lake. The greatest depth of the lake, in the broad portion between Évian-les-Bains and Lausanne, where it is just 13 km (8.1 mi) in width, has been measured as 310 m (1,020 ft), putting the bottom of the lake at 62 m (203 ft) above sea level. The lake's surface is the lowest point of the cantons of Valais and Vaud.[6] The culminating point of the lake's drainage basin is Monte Rosa at 4,634 metres above sea level.[7]