Overpumping groundwater for drinking water and irrigation has caused water levels to decline by tens of metres in many regions, forcing people to use low-quality water for drinking.
Most of those scientists, including Levy, still support water fluoridation as a proved method of controlling tooth decay, especially in populations where oral hygiene is poor.
Apparently what happened was that water collected on these tar pits and the bigger animals like the elephants ventured out on to the apparently firm surface to drink, and were promptly bogged in the tar.