The Oir, Scorff and Bresle river monitoring sites

The Oir, Scorff and Bresle river monitoring sites

Les 5 implantations U3E
  • The Bresle: in Normandy on the border between the Seine Maritime and Somme departments (length: 72 km / catchment area: 748 km²)
  • The Oir (pilot site): in Normandy in the département of Manche (length: 19.5 km / catchment area: 87 km²)
  • The Scorff: in southern Brittany in the Morbihan département (length: 70 km / catchment area: 480 km²)



These three "workshop" rivers have been monitored by INRAE and the OFB for over 40 years. They are all equipped with stations for monitoring the migration of diadromous fish and have been the subject of other recurrent biological monitoring since the 1980s.

The Oir site

Length: 21 km
Catchment: 86 km2

site atelier Oir

The Oir is a tributary of the Sélune, whose waters flow into the bay of Mont St Michel. Until recently, the upper reaches of this river were inaccessible to migrating fish, blocked some fifteen kilometres from the sea by two impassable dams, and only two downstream tributaries were usable for reproduction: the Beuvron and the Oir. The Oir is the most productive spawning tributary in the network.
Since 2021, with the removal of the two dams, the course of the Sélune has once again been accessible.
On the Oir, the flow of fish upstream and downstream is monitored all year round using the trapping facilities at the Cerisel mill in Ducey.


The Scorff site

Length: 70 km
Catchment: 480 km²

site atelier Scorff

The Scorff is a small Breton river that flows into the Atlantic Ocean at Lorient harbour. It is on the lower part of its main course, at the edge of the estuary and just at the end of the tidal influence zone, that the migratory fish monitoring station is located. Fish trapping activities (salmon, shad, lamprey, etc.) take place all year round.
Flows of upstream and downstream fish are monitored throughout the year using the trapping facilities at the Moulin des Princes.
The monitoring station at Pont Scorff is open to the public. It is designed to facilitate communication with a wide range of visitors.


The Bresle site

Length: 72 km
Catchment: 748 km²

La Bresle river

The Bresle is a coastal river in Normandy, rising in the Seine Maritime and flowing into the English Channel near Le Tréport.
Monitoring of migratory fish populations is based on double trapping. Fish are intercepted when they leave the river or enter it after their marine life phase. The monitoring station consists of two complementary devices, located respectively at Eu (76), 3 km from the sea, and Beauchamps (80), 15 km from the sea.
Fish trapping activities (salmon, lamprey, eel, etc.) take place throughout the year.


Modification date : 09 October 2023 | Publication date : 30 June 2015 | Redactor : U3E experimentation unit for aquatic ecology and ecotoxicology