Windermere is the largest of many picturesque lakes formed by the activity of the Pleistocene ice sheet in the Lake District National Park of northwest England. The park is studded not only with lakes but also with peaks including the highest in England (Sca Fell,978 m) and with historical and archeological relics, producing a very attractive landscape.

The lake is long and narrow from the north to the south, and an island in the central part divides the whole lake into the north and the south basin. Hilly highland stretches behind the shoreline and is used for grazing grounds and woodlands. There are two towns, Ambleside and Windermere, along the northeastern shore. The Freshwater Biological Association's Windermere Laboratory established in 1902 is situated in the midst of western shore.

There are so many lakes, Rydal Water, Grassmere, Esthwaite Water and so forth, in the drainage basin, and the water of these lakes flows into Windermere. Although the pH value of rain water in this area averages 4.4, that of lake water has been very stable since 1928 around 7.0. The present trophic level of the lake is mesotrophic, but eutrophication is proceeding gradually rowing to the influx of nutrients from farms and residential areas.