The water quality monitoring data on the Seine-Normandy basin between
1910 and 1993 are presented. Temporal and spatial variability were exa
mined for six parameters: ammonium, nitrates, chlorides, dissolved oxy
gen, biological oxygen demand and total coliforms? in 22 stations spre
ad over the Seine and the Marne rivers. The water quality parameters w
ere significantly altered from 1950 onwards, except for ammonium which
has been present since the beginning of the century in the lower cour
se of the River Seine. Despite all efforts, especially those focused o
n sewage treatment plant construction and enlargement, the Rivers Sein
e and Marne have not recovered the level of water quality of the forme
r century.