Lago di Lei is a reservoir in the Valle di Lei. The reservoir is almost entirely located in Italy, but the barrage was built on territory later assigned to Switzerland (municipality of Innerferrera, Grisons), while an equivalent territory north of the lake was assigned to Italy. The dam is operated by Kraftwerke Hinterrhein. The waters of the lake are the only waters in Italian territory which end up in the North Sea, being part of the Rhine's drainage basin.