The main tributary of the Sienne, the Airou winds its way for over 35km through the hard rock of a sinuous, steep-sided valley.The main tributary of the Sienne, the Airou winds its way for over 35km through the hard rock of a sinuous, steep-sided valley.
©The main tributary of the Sienne, the Airou winds its way for over 35km through the hard rock of a sinuous, steep-sided valley.|Syndicat Intercommunal d'Aménagement et d'Entretien de la Sienne
Sensitive natural areasThe Airou basin

The Airou basin

As you stroll through Beauchamps, you’ll come across the Airou basin, a Natura 2000 listed site. The Airou is one of the main tributaries of the Sienne. It meanders for 32 kilometers through a winding, steep-sided valley. The river is fed by numerous small tributaries.

The Airou basin

A Natura 2000 site

Home to four remarkable aquatic species, the Airou basin has been classified Natura 2000. Initiated by the European Union in 1992, Natura 2000 is a network of European sites. The aim is to guarantee a favorable conservation status for natural habitats and species of Community interest. There are over 1,750 such sites in France. Since 2007, the Syndicat Intercommunal d’Aménagement et d’Entretien de la Sienne (SIAES) has been responsible for managing the bassin de l’Airou site.

His main actions have been, for example, the implementation of a restoration and maintenance program for the Airou and its tributaries, agro-environmental measures (agricultural subsidies for farmers who manage their plots in a more extensive way) and the regional declination of the National Action Plan in favor of the Pearl Mussel.


A wealth of aquatic life


As the Airou boasts a remarkable wealth of aquatic life, the local fishing association has embarked on a property management approach to fish resources. No more restocking is carried out on the rivers of the Airou basin.

The Natura 2000 site was set up in this sector to preserve the habitat of four aquatic species: Atlantic salmon, planer lamprey, sculpin, pearl mussel.

Other species such as brown trout, minnow, gudgeon and eel can also be observed. Very rarely, sea lampreys, sea trout and white-clawed crayfish have also been spotted.

Atlantic salmon

This migratory fish can grow to over a metre in length. As an adult, it frequents the waters of the Airou to reproduce. The young then spend 1 to 2 years in the river before reaching the sea. Every year, around a thousand salmon return to the Sienne basin to spawn.

The best times to observe salmon are autumn and winter. In autumn, salmon will take advantage of heavy rainfall and rising water levels to make the last few kilometers of their migration. In winter, they can be observed directly on the spawning grounds where they reproduce. On the Airou, these spots generally correspond to the fast-flowing currents.

Please note that salmon fishing is prohibited on the entire Airou.

Glacier lamprey

This fish has a serpentine body. Its back is yellowish-brown and its belly is pearly white. It measures between 15 and 20 centimeters. It lives exclusively in freshwater and frequents the sandy portions of the Airou.

After reproduction, the adults die. The eggs are covered by sand and develop over a fortnight. The larvae then bury themselves in the sand and only emerge after 5 to 7 years to metamorphose and live in the water.

The gliding lamprey is easiest to observe in spring. The larvae have emerged from the sand in autumn and the streams are lower. This is also their breeding season.

The sculpin

This fish measures between 10 and 15 centimeters. Its club-shaped body is gray-brown with dark transverse bars. It likes cool, well-oxygenated running water. The sculpin is carnivorous, feeding on larvae, small invertebrates and even trout eggs, for example.

The sculpin lives in the middle of or under rocks with which it blends. They remain discreet during the day. In the morning and at dusk, they are much more active as they search for food.

The pearl mussel

This freshwater mollusc is renowned for its exceptional longevity (around 100 years). Although protected, it is now on the brink of extinction. This mussel also has the particularity of producing jewelry pearls.

The life cycle of the pearl mussel is linked to that of the fario trout and Atlantic salmon. The larvae develop exclusively in the gills of these two fish. Once the larva has become a small 0.5 mm bivalve, the mollusc detaches and continues its growth at the bottom of the river. The pearl mussel filters the water and feeds on particles of organic matter.

At present, the pearl mussel population in the Airou basin is the only one known in the Manche département. To enhance its protection, a European LIFE+ program “Preservation of the Pearl Mussel in the Armorican Basin” is currently underway in the Airou basin and five other rivers in Normandy and Brittany. It aims to cultivate pearl mussels and maintain, or even develop, real living rivers for the survival of this species.

The Natura 2000 site “Bassin de l’Airou” crosses 13 communes representing 710 hectares: Beauchamps, Bourguenolles, Champrépus, La Haye-Pesnel, La Lande d’Airou, La Meurdraquière, La Trinité, Le Mesnil-Amand, Le Mesnil-Rogues, Le Mesnil-Villeman, Le Tanu, Rouffigny and Ver.

This site is part of the Sienne watershed.

The main activity on this watershed is dairy cattle farming. On the Airou basin, agricultural plots are mainly used as pasture or hay meadows. Cultivated plots are mainly located on the plateaus outside the site. On the contrary, the Airou’s major bed and slopes are largely covered by natural meadows or by wood when the slopes are too steep.


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