Anglo American was also accused in 2007 of damaging environmental practices: in order to complete its planned Alaskan Pebble Mine in collaboration with Northern Dynasty Minerals, the company considered building a massive dam at the headwaters of the world's largest sockeye salmon fishery, which it would risk obliterating. Opponents also pointed to the use of cyanide, heavy metals, and acid mine drainage which can all have potentially devastating effects on the environment of the Bristol Bay area. Opponents of the Pebble Mine created Ballot Measure 4 to impose additional water quality standards on new large-scale mines in the state. However, in August 2007, Alaskans voted against the initiative. As of September 2008, the Pebble Limited Partnership had not yet put forward a project proposal and was working to prepare a prefeasibility study for the project in the second half of 2009. The mine proposal would still need to undergo environmental studies and the permitting process, including being subject to state and federal water protections. In December 2013, Anglo American withdrew from the Pebble Limited Partnership.