Windermere (sometimes tautologically called Windermere Lake to distinguish it from the nearby town of Windermere) is the largest natural lake in England. More than 11 miles (18 km) in length, and almost 1 mile (1.5 km) at its widest, it is a ribbon lake formed in a glacial trough after the retreat of ice at the start of the current interglacial period. It has been one of the country’s most popular places for holidays and summer homes since the arrival of the Kendal and Windermere Railway’s branch line in 1847. Forming part of the border between the historic counties of Lancashire and Westmorland, Windermere is today within the administrative county of Cumbria and the Lake District National Park.