My sister and her husband have a pond at their farm that they use for swimming - it even has a beach. They add some kind of blue coloring to it. I think it comes in a 5 gal. bucket.
I've read that on their website. I've used it in fountains and garden ponds. I've rinsed my white cats in it after their baths. I've used it on my own hair back when it was platinum (many moons ago...I looked like Eminem)