In this task, you're given a context passage, followed by a question that needs to be answered. Based on the paragraph, you must write unambiguous answers to the questions and your answer must refer to a specific phrase from the paragraph. If multiple answers seem to exist, write the answer that is the most plausible.

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 ?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Because the pit was contaminated .