Oir

Until recently, the upper reaches of this river were inaccessible to migratory fish, which were blocked some fifteen kilometres downstream by two impassable dams. Only two tributaries located further downstream were suitable for spawning: the Beuvron River and the Oir River. The latter is the most productive spawning tributary in this river system.
Since 2021, with the removal of the two dams, the course of the Sélune has once again become accessible. On the Oir, the flow of fish moving upstream and downstream is monitored throughout the year via trapping facilities at the Cerisel mill in Ducey.

Monitoring activities for migratory fish are the subject of an annual presentation:

Presentations : 2018 - 2017 - 2016 - 2014 - 2013 - 2012 - 2011 - 2010 - 2005

The Oir River, which is 21 km long and flows east to west, has an average gradient of 11‰. It drains a catchment area of 87 km², consisting of sedimentary and metamorphic schist terrain with a few granite outcrops. The water is close to neutral and of acceptable quality, but with high nitrate levels. Human activities in this catchment are primarily agricultural (grassland, fodder crops, dairy herds).