The Lac de Guiers or Lake Guiers is a lake in northern Senegal, south of the city of Richard-Toll and in the Louga and Saint-Louis regions. It is a chief source of fresh water for the city of Dakar, hundreds of kilometers to the south-west, through underground pipes. The shores are mostly fertile. The north shore and surrounding area have been converted to a large sugar-growing region irrigated with water from the lake.