During winter, the temperature of the water overlying the shallow, typically 2--5 m deep, 'shelf' region around the edge of the 310 m deep Lake Geneva falls more rapidly than that over deeper areas. This causes the spilling or 'cascading' of relatively dense water from the shallows down the sloping sides of the lake in the form of gravity currents, 2--15 m thick and typically 0.1 ¿C cooler than the ambient. The flow is intermittent with 'slugs' of cold water lasting, on average, for 8 hrs with mean downslope speeds of 5.2 cms-1. The temperature and thickness of the slugs is however variable, with pulses of colder water lasting for 1--3 hrs, each preceded by a 'front' in which thickness increases and temperature falls by about 0.01 ¿C per min. The net volume flux carried by the 'slugs' is 18.5 times the mean winter flow into the lake from rivers. ¿ 2001 American Geophysical Union