Bolin Island is man-made. It was built to be a defended lake dwelling between 500 and 1000AD. They were made by people who farmed the land near the lake.
These artificial islands were called crannogs (from crann, the Irish word for a tree) because of the large quantity of wood that survive on the water-logged sites. Bolin Island is just 30 metres across could only have supported a single household.
