The Porgera mine empties millions of tons of tailings and mountains of waste rock directly into the nearby 800 km-long river system. The waste enters the Porgera River, which drains into the Lagaip River then into the Strickland River and eventually into the Fly River before reaching the Gulf of Papua. The upper reaches of the river system are fast flowing and steep while about 200 km downstream the river enters an extensive flat floodplain where it meanders. Dumping into this major river system began in 1992 and has continued ever since - source.
The extreme damage this mine waste disposal method is causing, as well as concerns about likely environmental toxicity from metals in the mine waste, has been well-documented - source