Windermere is a ribbon lake. (Ribbon lakes are long, narrow and finger-like.) It was formed 13,000 years ago during the last major ice age by two glaciers, one from the Troutbeck valley and the other from the Fairfield horseshoe. When the glaciers melted the lake filled with the meltwater, which was held in by moraine (rock material) deposited by the glacier.
The lake is drained from its southernmost point by the River Leven4. It is replenished by the rivers Brathay, Rothay, Trout Beck, Cunsey Beck and several other lesser streams. The lake is largely surrounded by foothills of the Lake District which provide pleasant low-level walks; to the north and north-east are the higher fells of central Lakeland.