Tuff - at the origin of the eponymous waterfall of Planches-près-Arbois in Jura - is a very friable sedimentary rock that is easily degraded by all kinds of external aggressions, such as trampling. For this reason, it is strictly forbidden to walk in the water, splash or swim around the waterfall. Tuff is part of the geological heritage of the Jura and the remarkable site of Planches-près-Arbois is classified as landscape and protected by a biotope decree.