The Lake of San Casciano is an artificial lakeside basin on the border between Tuscany and Lazio, and is also not far from Umbria.
Located at the south-eastern limits of the province of Siena, the lake extends south of Mount Cetona, a few kilometres south-west of San Casciano dei Bagni, and has a somewhat irregular shape, with the southern shore marking the border with Lazio (province of Viterbo). The lake is the most northerly point of Lazio.
