It was not until the 1990s that serious efforts to clean up the Berkeley Pit began . The situation gained even more attention after as many as 342 migrating geese picked the pit lake as a resting place , resulting in their deaths . Steps have since been taken to prevent a recurrence , including but not limited to loudspeakers broadcasting sounds to scare off waterfowl . 
Question: What's a possible reason the geese died at Berkeley pit ?
Because the pit was contaminated .