It may also be one of the most polluting. Along with the rock waste, the mine dumps heavy metal sulfides and hydroxides, including ferro-cyanide complexes and Jarrosite, directly into the Maiapam at levels up to 3,000 times PNG's normal legal limits.
Sediment loads are a clear threat to subsistence gardens and fisheries along the river.
The PNG environment minister initially rejected the environmental plan submitted by Porgera in 1989, but relented after studies showed the lack of economically viable alternatives. But five years after operations began, clear impacts on the health and welfare of local people, wildlife and the riverine environment have put pressure on the government to reconsider. In 1995, Dr. John Konga, at Sopas Hospital in the area, confirmed a death which he believes could have been caused by arsenic poisoning. Arsenic, one of the pollutants from the Porgera mine, can now be found at levels many times the pre-mine level in the Strickland River system. Zinc, lead and mercury are also now present at levels three to 3,000 times the Australian and Papua New Guinean standards at various distances downstream from the mine's discharge point.