Rachel told the story tonight of the inviting blue water in and English quarry that is actually toxic with a pH level of 11.3, "almost equivalent to swimming in bleach." But despite posted warnings, including pointing out that the water contains a number of dead animals and car parts, people couldn't resist and still jumped in - surely to great regret. So town officials addressed the real source of the problem, the water's tempting color, and dyed it black. That seems to have worked, but doesn't the whole affair seem like a metaphor for something else? Helping people who can't stop themselves by taking away temptation for them? Does that describe a political story you can think of?
The color (and presumably the pH) is reportedly the result of caustic chemicals in the quarry stone. Here's Google's satellite view of it. That's no trick of the light.