Awful smell in basement?

This awful dead skunk-like smell just started coming through the heat exchanges. When I go in my basement, the whole thing reeks like skunk. It is the middle of winter here, however, we are having a warmer spell and the snow outside is melting. We have a sump pump in the basement the is emptying every few minutes due to drainage, apparently we sit on a high water table. Is that causing the smell? Or should I be worried about something else?