Water Quality
Periodically the sewerage systems of Paris experience a failure known as sanitary sewer overflow, often in periods of high rainfall. Under these conditions untreated sewage has been discharged into the Seine. The resulting oxygen deficit is principally caused by allochthonous bacteria larger than one micrometre in size. The specific activity of these sewage bacteria is typically three to four times greater than that of the autochthonous (background) bacterial population. Heavy metal concentrations in the Seine are relatively high. The pH level of the Seine at Pont Neuf has been measured to be 8.46. Despite this, the water quality has still improved, with several historians having called it at various times in the past as an "open sewer".
In 2009, it was announced that Atlantic salmon had returned to the Seine.
Read more about this topic: Seine
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