Janet's Foss is a small plunge waterfall on Gordale Beck, tucked within a secluded wooded dell near the village of Malham in the Yorkshire Dales National Park, North Yorkshire.

The beck drops over a hard limestone outcrop coated in tufa — a spongy, moss-covered deposit built up over time as lime-rich water dissolves and redeposits calcium carbonate — into a deep pool below.

The surrounding woodland is noted for spring carpets of bluebells and wild garlic, and the site is owned and managed by the National Trust.

Local folklore holds that "Janet" (or Jennett) was the Queen of the Fairies, said to inhabit a small cave behind the fall — a legend that suits the waterfall's enchanting, green-glowing setting.

The pool was historically used for sheep dipping, a communal event for the village, and today draws wild swimmers. The word "foss" derives from the Nordic term for waterfall.