Water Quality and Fisheries Impacts of Mining in the North Fork Coeur D'alene River Subbasin, Idaho

The North Fork Coeur d’Alene River Subbasin is a forested watershed in the Rocky Mountains of north Idaho encompassing the northern portion of the Coeur d’Alene Mining District, historically one of the richest mining districts in the world. Gold was discovered here in Prichard Creek in the early 1880s. A boom of railroads, towns, mines, and mills soon followed. In the early days, placer deposits of gold were mined by various means including hydraulic mining and floating dredge. Later, underground mines for zinc, lead, and silver were developed throughout the mining district. The largest and most productive of these mines were in the South Fork Coeur d’Alene River Subbasin, now known as the “Silver Valley” – home to one of the United States’ largest mining-related Superfund sites, the Bunker Hill Mining and Metallurgical Complex.

Located just north of the divide from this “mining megasite,” mining and associated environmental projects have continued in the North Fork Coeur d’Alene River Subbasin. The large underground mines and associated mills have closed, and many are abandoned. The large floating dredge stopped in 1926, leaving 5 miles of dredge-spoil piles. Today, small placer gold dredge mining operations continue, only one underground gold mine is currently operating, and exploratory drilling is common. Impacts of present-day mining are mitigated by state and federal regulatory requirements though compliance remains challenging in remote areas. Total maximum daily loads (TMDLs) developed under the Clean Water Act (CWA) are implemented through permit programs, best management practices, and other water quality improvement projects. These efforts are complemented by hazardous waste remediation and removal actions under Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund). Extensive environmental cleanup has occurred, but the legacy of historic mining and present day operations continue to challenge water quality and fisheries in these watersheds.

Fisheries concerns are focused on native trout including bull trout and westslope cutthroat trout. Bull trout are likely extirpated from the subbasin, but recent critical habitat designations include some of these waters. Both native trout species face increasing colonization by brook trout along with water quality impairments and habitat degradation. Idaho Department of Environmental Quality (DEQ) assessed water quality in the area and identified 104 miles of fish habitat in the Prichard and Beaver Creek drainages as “not fully supporting” cold water aquatic life. Mining-related causes of these impairments include sediment, temperature, cadmium, copper, lead, nickel, zinc, flow alteration and habitat alteration.