Why do fish die in the winter?

Nate's Fishing Blog has a excellent but sort of long post that gives the answer. Nate runs a pond management business and knows his stuff. Basically it is a post about why winter kills happen and I found his thoughts highly interesting.

Money quote:
After all this rambling, the answer to the question of what causes fish to die in the winter is simple: they either suffocate to death, or they end up on my dinner plate. Both of these causes of death will end the life of thousands of fish every winter.