About this place
The Réserve naturelle nationale de la frayère d'Alose is a small but remarkable nature reserve on the Garonne River, straddling the border between the towns of Agen and Le Passage in the Lot-et-Garonne department of southwestern France. Established in 1981, it covers roughly 48 hectares and protects a 2.31 km stretch of the river — running from about 800 meters upstream of the Pont de Pierre to just past the aqueduct bridge in Agen. Unlike most French nature reserves, it doesn't include any riverbanks at all: the protected zone consists purely of the river channel itself, sitting right in the middle of an urban agglomeration — a setup shared by only a small fraction of France's national nature reserves.
Why was this stretch of river protected?
The reserve exists to protect the allis shad (Alosa alosa), an anadromous migratory fish that spends most of its life at sea but swims upriver for a few months each year to spawn in fresh water. This particular section of the Garonne, thanks to the variety of riverbed textures and currents found here, is one of just three privileged spawning grounds for the species along the entire river. Shad eggs and juveniles are extremely sensitive to environmental disturbance — floods, water temperature swings, sediment shifts — as well as to human interference, which is exactly why this short but critical stretch of river received formal protection.
Allis shad populations, once abundant across European rivers, have struggled to recover in recent decades, and the species is now considered critically endangered. France remains one of the last countries where meaningful populations of this fish still survive, though numbers continue to decline even here.
What lives in the reserve?
Although the protected area is limited to the river channel, its ecological value extends well beyond the shad itself. Researchers have identified 167 species across eight different taxonomic groups within the reserve's boundaries — spanning fish, aquatic invertebrates, and birds tied to the riverine environment. Despite its modest size, the reserve functions as an important ecological corridor running straight through the heart of an urbanized stretch of the Garonne valley.
Who manages the reserve?
Since 1986, management of the reserve has been entrusted by the Prefect of Lot-et-Garonne to the Association pour la Gestion de la Réserve Naturelle de la Frayère d'Alose. The association's work covers scientific monitoring of fish populations, on-the-ground protection and surveillance, and public outreach — raising awareness among residents and visitors about the allis shad and the broader role France's nature reserves play in protecting river ecosystems.
Frequently asked questions
Where exactly is the reserve located? On the Garonne River, between the towns of Le Passage and Agen in the Lot-et-Garonne department, covering about 2.31 km of the river's course.
Which species is the main focus of protection? The allis shad (Alosa alosa), a migratory anadromous fish that travels from the sea into the Garonne to spawn.
When was the reserve created? In 1981, with management handed to a dedicated local association starting in 1986.
Does the reserve include the riverbanks? No — unlike most French nature reserves, this one protects only the river channel itself, which makes it unusual on a national scale.
Sources:
Nearby places
Earn badges for the places you visit
Download NextOnTrip, discover new places and check off your trails.