Windermere is a ribbon lake located in Cumbria, England, within the Lake District national park. It holds the distinction of being the largest lake in England by length, area, and volume, though it remains considerably smaller than the largest Scottish lochs and Northern Irish loughs. Administratively, the lake falls entirely within the Westmorland and Furness unitary authority area as of April 2023, having previously been part of the historic boundary between Westmorland and Lancashire.

The current lake formed after the Last Glacial Maximum during the retreat of the British and Irish Ice Sheet between 17,000 and 14,700 years ago. Historically known as Winder Mere or Winandermere, the name likely translates to 'Winand or Vinand's lake.' The area has been popular with tourists since the Kendal and Windermere Railway branch line opened in 1847, which facilitated access to this previously remote glacial valley.

The lake features two separate basins influenced by distinct geology, with hard volcanic rocks in the north and softer shales in the south. It contains eighteen islands, the largest being Belle Isle, formerly known as Lang Holme. The surrounding area includes the village of Windermere, which did not exist before the railway arrival, and Bowness-on-Windermere, the only settlement directly on the lakeshore.

Tourism is a central feature, driven by the lake's scenery and extensive boating services that operate from Lakeside to Waterhead. The Freshwater Biological Association was established on the shore in 1929, contributing significantly to early work in lake ecology and limnology. Visitors can explore heritage sites such as the Windermere Steamboat Museum, which houses boats dating from 1200 to 1907, and various gardens and historic houses.

The town of Windermere has a population of 4,800 people as of 2021. It serves as a hub for transport connections, with a railway station linking to Oxenholme on the West Coast Main Line. The economy relies heavily on tourism, supported by local amenities including supermarkets and restaurants. The area offers year-round appeal, with boat services and museums operating throughout the seasons.