From National Geographic:

When antidepressant pills get flushed down the drain, they do more than create happier sewers.

Scientists in Erie, Pennsylvania, have found that minute concentrations of fluoxetine, the active ingredient in Prozac, are killing off microbial populations in the Great Lakes.

Traces of antidepressants such as Prozac have been found in both drinking and recreational water supplies throughout the world, in quantities experts say are too dilute to affect humans but which have been found to damage the reproductive systems of mollusks and may even affect the brains of animals like fish. Read more.