"It's the first time this species has been identified just outside Paris," said the authority in charge of cleaning up the river, SIAAP.
The capture of a sea trout, a migratory fish "sensitive and demanding about the quality of the water" in which it swims, underlines the continuing improvement in the waters of the Seine, SIAAP added in a statement.
It swam upstream from the Seine estuary on the Atlantic ocean through a great number of locks and barriers, bringing to 32 the number of fish species in the Seine, in comparison to only three in 1970.