Pertes de la Valserine, Limestone slot canyon in Valserhône, France

Pertes de la Valserine is a slot canyon on the Valserine at Valserhône, just upstream of its confluence with the Rhône. The river crosses a limestone slab and has cut a deep channel between rock walls up to thirty metres high, with potholes scoured into the stone. Despite the name, the water does not sink underground; it is simply hidden between the narrow walls.

The site has been a protected natural monument since its inscription on 2 February 1937. The Valserine cut its channel here through a limestone slab, forming a slot canyon rather than a true underground loss, and the name likely arose because the water, sunk between walls up to thirty metres high, is hard to see from the banks.

The name "pertes" is misleading: the water does not sink into the ground but is simply hard to see from the banks, hidden between rock walls up to thirty metres high. The site has been a listed natural site since 2 February 1937 and receives about 50,000 visitors a year.

The site is open from spring until the start of winter. A waymarked path reaches it from Bellegarde-sur-Valserine or from Lancrans; the canyon walls rise up to thirty metres, so the water is often hidden from the banks.

The name is misleading: the Valserine does not sink into the ground here. The water simply drops out of sight between rock walls up to thirty metres high, which is why it was called a "perte". The river has also bored giant's kettles into the limestone slab it crosses.