The region around the Chiemsee is Chiemgau and is a famous recreation area.
The Chiemsee was formed, like many other pre-alpine lakes, at the end of the last ice age about 10,000 years ago from a hollow carved out by a glacier (a Zungenbecken). Originally the lake covered an area of almost 240 km2 (93 sq mi), which is about three times its present area. Within 10,000 years its area had shrunk to around 80 km2 (31 sq mi). Before 1904 the water level was lowered by about a metre. As a result, large areas of dry land were reclaimed.
There are three main islands on the lake: Herreninsel, the largest, with an area of 238 hectares (590 acres); Frauenchiemsee, 15.5 ha (38 acres), also called Herreninsel ("gentlemen's island") and Fraueninsel ("ladies' island"); and uninhabited Krautinsel, 3.5 ha (8.6 acres). It is known as "Cabbage Island" because in the Middle Ages it was cultivated with cabbages and other vegetables.
There are also three very small islands: the Schalch, to the west of Frauenchiemsee; and two unnamed islands, 54 and 80 meters south of the Krautinsel, with an area of 30 square metres (320 sq ft) each.