x2: The fish population of the Seine has become diverse since 1990 (33 species versus 15)

The Seine is now classed in the category “good state of fish populations” by the national River fish indicator. This is the result of intensive work carried out over the long-term by the public and private actors of the Seine basin. Pollution has been reduced, fish passes built, fish censuses performed, and regular monitoring carried out to improve water quality. In particular, the Paris interdepartmental water treatment board (SIAAP) was the instigator of the MeSeine measurement network set up to study the physicochemical and bacterial quality of the river water. Other initiatives provide water users with information on the quality of the river. One example is the “River Quality” application developed in 2013 at the initiative of the Water Boards and the French Biodiversity Agency. In just a click, one can discover the fish life of the river and its ecological state. As for the scientists of PIREN-Seine, they have developed a global fish species distribution model on the scale of the Seine basin, based on data collected from 269 stations. Such models allow determining the most propitious zones for the development of certain species and forecasting the impact of environmental changes.

In spite of these positive results, the habitat remains fragile. Although ecological continuity has been restored, the Seine has large quantities of micropollutants that are difficult to eliminate. They can be highly toxic at low doses and alter the metabolic functions of the fish. It is therefore vital to continue efforts to treat drainage water and make companies and the neighbouring population aware of the ecological impacts of their activities.