Lake Cadagno (Italian: Lago di Cadagno) is a meromictic lake in the Piora valley (canton of Ticino), Switzerland. As one of a few meromictic lakes in Europe, it is the object of numerous scientific studies. The Piora valley - located in the Gotthard massif (central Swiss Alps) in the Southern part of Switzerland near Airolo at an altitude of 2000 m above sea level - is a landlocked alpine valley whose scientific value has been recognized for more than two centuries.