Since 1995 deformed frogs have been turning up. Call them the canaries in the coal mine for environmental health. Frogs are showing signs of some kind of stress.
So is it a parasite? Pollution? A natural phenomenon? Cannibalism? Fungus? Ultraviolet light? Something in the water?
Video from YouTube
The tap water data referred to in the video in which they placed embryos in tap water collected from different sites in Minnesota resulting in deformities was later deemed inconclusive upon review. To date, researchers are still debating about the cause of the deformities (MPRNews). More recent research in 2009 has shown that dragonfly nymphs and stickleback fish may be eating frogs legs. I hear they are pretty tasty (MinnPost).
The real answer is likely a combination of factors.
Minnesota Pollution Control Agency