The basin of the Zmulner See has its origin in the setting off of a side branch of a large dead ice-rock out of the glacier that retired in the Glantal to the west. The flat range directly in the north- west of the lake is formed by ground moraines. Surrounded by a partly narrow belt of reed the lake is situated within an intensively used agricultural area.
Landscape protection area. The Greenland in the west of the lake that formerly was intensively used, too, was taken out of use by a project of ecologization. The color of the water is a bit brownish, because of the surrounding wet- and moor areas. The lake drains into the Glan in the north. The Zmulner See landscape protection area is about 40 ha (LGBl. 81/ 1970).