Here’s a neat article from National Geographic – Salmon are returning to the once heavily polluted Seine river. This just goes to show how we can correct our mistakes – it’s never too late. Over the past three decades scientists and urban planners have managed to dramatically reduce industrial discharges and levels of heavy metals such as mercury, lead and copper in the Seine river, and nature has responded in kind. While in 1970 there were just three species of fish, there are now believed to be 32.

This year at least a thousand Atlantic Salmon passed through Paris along their migratory run—exceeding “anything we could imagine,” Bernard Breton, secretary general of France’s National Federation of Fishing, said via email. The Seine once had a robust population of the fish. But pollution that began in the late 1800s killed most of them off, and today salmon are on the European Union’s endangered species list.

After a 25-year effort to cleanse the toxic river, its waters are again attracting the fish, which begin their annual journey about 93 miles (150 kilometers) away in the Atlantic Ocean.

Salmon had disappeared from the Seine by 1900, and most fish species saw a similar demise by 1920. Before 1995 between 300 and 500 tons of fish, including salmon, were dying each year in the river, Breton said.

By 1995 only five species of fish—hardy species such as carp and eel—called Paris home. Now, thanks to the cleanup, 32 species of fish live in the Seine. The reappearance of Atlantic salmon is the most important “living proof” that the water has gotten cleaner, Breton said.

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