Lake St. Moritz (German: St. Moritzersee, Romansh: Lej da San Murezzan) is a lake near St. Moritz, Switzerland. With a surface of 0.78 km², it is smaller than the main lakes of the Upper Engadin valley (Lake Sils, Lake Silvaplana).Every January or early February, Polo matches are held on the lake. Compared to polo played in the summer, a slightly larger and lighter red ball is used that is easily visible in the snow.For three weekends every February, horse races are held on the frozen lake.