Wast Water or Wastwater is a lake located in Wasdale, a valley in the western part of the Lake District National Park, England. The lake is almost 3 miles long (4.6 km) and more than a third of a mile (600 m) wide. It is the deepest lake in England at 258 feet (79 m), and is owned by the National Trust. It is one of the finest examples of a glacially 'over-deepened' valley.