Bavaria's biggest lake, Lake Chiemsee, is also known as the "Bavarian Sea", although it is actually the remains of a glacier. It is 18 kilometres long, 14 kilometres wide and covers an area of 85 square kilometres. The Tyrolean river Ache and the Prien feed Lake Chiemsee, and the Alz drains it, running from near Seebruck, where the Roman fort of Bedaium once stood. To the south, the Lake is flanked by the Kampenwand, Hochgern and Hochfelln mountains with their distinctive profiles. The Herreninsel, Fraueninsel and Krautinsel islands lie close together in the calm waters.