One hundred kilometres long, the Authie has cut a green valley which separates the Somme from the Pas-de-Calais. It flows into the Channel, at Fort Mahon, about 20 kilometres north of the Somme Bay.

The Authie has two sources, both of them in the Somme, at Coigneux and at Coin. The one at Coigneux has been developed. The panels erected near the low wall that protects the source give you information about the river.

The water of the Authie is of high quality. It is an ideal river for Salmonidae: trout and salmon will soon be able to return to the sources, thanks to the development work in progress on some of the weirs.

Whereas the upper valley is wooded, the middle valley, which is more steep-sided, offers a succession of spinneys, marshes and arable land. The low houses in the hamlets that line this valley are abundantly decked with flowers. A visit to the Valloires Gardens at Argoules, which extend for 8 hectares down to the river, is an absolute must.

Authie Bay is a vast estuary that has remained wild, between Fort-Mahon and Berck. A signposted footpath for exploring the dune environment stretches for 1.5 kilometres across the Authie dune, which is the property of the Conservatoire du Littoral (Coastline Preservation Agency). A little further on, the sea wall that protects the Bay offers a magnificent view of the estuary.

The Environment Agency (CPIE) of the Authie Valley organises outings to explore the valley, on foot, mountain bike or by canoe. These outings give you the opportunity to learn how to read the landscapes and appreciate the wealth of flora and fauna of the different environments.