Wasdale (/ˈwɒzdeɪl/; traditionally /ˈwɒsəl, ˈwɒʃdəl/) is a valley and civil parish in the western part of the Lake District National Park in the Cumberland district, in the ceremonial county of Cumbria, England. The River Irt flows through the valley to its estuary at Ravenglass. A large part of the main valley floor is occupied by Wastwater, the deepest lake in England (258 feet or 79 metres). In 2021 the parish had a population of 127.

On the south-eastern side of the lake are very steep screes below the summits of Whin Rigg and Illgill Head which are more accessible on the far side. The head of the valley is dominated by the Great Gable and Scafell Pike, the highest peak in England, which, along with Scafell, Kirk Fell and Yewbarrow, surround the small community of Wasdale Head. Wasdale is famous amongst rock climbers as the home of British rock climbing. A classic route is Nape's Needle on Great Gable.

At the hamlet of Wasdale Head is St Olaf's Church, one of the smallest churches in England.

Further down the valley are the villages of Strands and Gosforth.^{[citation needed]}

Clockwise from the north-west:-

Sty Head Pass

The name came from Old Norse Vatnsdalr, which means "valley of the water". The alternative spelling "Wastdale" existed through much of the nineteenth century.

The civil parish of Wasdale was historically a chapelry called Nether Wasdale within the larger ancient parish of St Bees. Nether Wasdale became a separate civil parish under the Poor Law Amendment Act 1866. The name of the civil parish remained Nether Wasdale until 2000, when it was changed to Wasdale.