The Copper Bluff Mine is located within the Hoopa Valley Tribal Reservation in Hoopa, CA. Metals from the mine could be hazardous to the tribal subsistence fishery in the Trinity River, which provides habitat for federally threatened Coho Salmon. Tunnels that were used to transport ore and other mining material now allow acid mine drainage to flow into the Trinity River. Acid mine drainage occurs when groundwater contacts minerals inside the mine and reacts to create sulfuric acid. This drainage can be toxic to people and aquatic life.