In most shopping malls, garden centres, parks etc where there are ponds or running water it often seems people are encouraged to throw a coin in which will be collected later for charity. I’ve noticed all sorts of other watery places, out in the middle of nowhere sometimes, where people do the same thing… this must be such an age-old custom that it probably goes right back to when ancient peoples made offerings to gods and spirits who lived in or near water… I don’t have any evidence for this, it’s just an idea, but in the old days people might throw in a weapon, or pieces of metal for example. They would have done it with some specific purpose or understanding of what they were doing, we do it out of some vague superstition that a wish we make might be granted.
We were at Þingvellir national park in Iceland, and passing by this water, there were silvery coins on the bottom… most of us rifled through our pockets and found something. The water is called Peningagjá, and people have been doing it for hundreds of years, making a wish which apparently will be granted if you are able to see your coin dropping down through the crystal clear water to the bottom. This is the only place people should do it… but I guess many visitors don’t know that and drop their coins in other places too.

