I listened to a report on this topic on NPR today. They said that Greek yogurt whey has less protein than the whey produced by making cheese or other dairy products, but is more acid and has a lot of sugar. Almost all the GY produced in the US comes from two plants in the same general area in upstate New York. The GY whey is not suitable for use in other food products, or animal feed. If dumped into the river system it would feed bacteria that would result in water contamination and fish die-off. Fortunately, the Fage plant is near a treatment plant that can turn the whey into biodiesel, but the demand for GY has led to production of more whey than the plant can process. Whey from the Chobani plant is trucked away and eventually combined with manure to become fertilizer. However, there's a limit to the amount of this type of fertilizer that farmers can use without contaminating run-off. So at present, whey has to be trucked greater and greater distances to facilities that can process it for either fuel or fertilizer. This is raising GY production costs and may possibly impact GY availability in the future.