In days of yore, the great cities of the world were founded on great rivers: London on the Thames, New York on the Hudson, Paris on the Seine. Of course, those rivers were eventually fouled beyond recognition -- more open sewers than rivers -- with every type of pollutant imaginable, and some that aren't.

Within the last several years, however, clean-up campaigns led by environmental groups have turned the tide, and now you can safely swim in the Hudson River (as I did myself just a few days ago).

Paris, too, has been cleaning up the Seine – fish disappeared from her waters in the 1920s. And the effort is showing one exciting result: Atlantic salmon have returned to the Seine. Parisian chefs still can’t cook le saumon -- levels of pesticides and heavy metals in the water remain high -- but the Atlantic salmon is known as a picky swimmer, and will only swim up channels that are clean enough to safely spawn in. That’s encouraging news for continued clean-up efforts worldwide.

What’s going on in your local waterway?