It is REALLY concentrated in the bottle, so you could dye just about anything (including YOU if you get any on you while you're pouring). Once in the water, it dissipates pretty quickly. You can swim in the water immediately, though I think I would avoid the spot where it is spreading from for a while. Once the water is blue, you can't really see the color on you when you get out and dry off. I haven't noticed any blue feathers on the water fowl yet/w3tcompact/icons/wink.gif.