Ophidian Oddity

While on a walk alongside a frozen pond this morning, I came across this northern water snake.  I didn't go onto the ice to look, but from where I stood, it appeared intact and without injury.  Not sure what would cause a snake to come out of hibernation with temperatures as low as they've been.  This is the second unusual happening at this pond lately.  A few weeks ago, I noticed that dozens of bullfrog tadpoles were floating tail-less in the water.  Did a predator go into a feeding frenzy and dine on tender tails, or did a sickness cause them to die off?