Month: February 2026
THE DIRT: Historic pollution study of the Coeur d’Alene Basin Pt.4
By the early 1930s, much of the Coeur d’Alene River was effectively lifeless. Fish had disappeared, plankton was dying, and long stretches of the river showed little sign of recovery. In 1933, federal scientists confirmed that mine-contaminated water was deadly to aquatic life—but their most alarming discovery came when they looked beyond the water itself, to what remained behind.
The greatest danger lay in the hard mineral build up that formed on mine wastes exposed to moisture, light, heat, and oxidation. Samples collected from Smelterville Flats and Thompson Flats were chemically distinct from other waste materials and quickly identified as highly toxic.
Goldfish were used extensively in these experiments due to their resilience, despite not being native to the watershed. Even very small amounts (0.01%) of the Thompson Flats material caused fish to release large amounts of slime. At higher concentrations (0.18%), fish became weak, lost control of their movements, and could no longer swallow. Prolonged exposure resulted in black lead deposits forming in the fins, followed by death.
In lower-concentration tests where the material was allowed to settle, mucous production subsided and fish often recovered within days. This pattern revealed a critical mechanism: when disturbed or suspended—such as during floods—the material became deadly.
Further testing across multiple species showed that zinc caused fast, immediate harm, while lead caused damage that built up over time. Even when polluted water was heavily diluted—just one part contamination mixed into 100,000 parts clean water—it stopped digestion in fish, frogs, and turtles, permanently altered heart function, and killed all plankton within 24 hours. Comparative studies showed incrustations from Smelterville Flats to be even more toxic than those from Thompson Flats.
Based on this evidence, Ellis concluded that mine wastes discharged into the South Fork in the Wallace–Kellogg area had rendered more than 50 miles of the South Fork and main Coeur d’Alene River effectively barren—devoid of fish, plankton, and aquatic food sources. He warned that massive deposits of toxic materials along riverbanks and floodplains would continue to poison the river and threaten downstream waters, including Lake Coeur d’Alene itself. Even if discharges ceased, recovery would take time.
Ellis did not call for an end to mining. Instead, he concluded that the only way to prevent pollution-related harm to fisheries was to keep all mine waste out of the Coeur d’Alene River. He pointed to successful waste-management systems in Kimberly, British Columbia, where tailings were routed to settling basins before treated water was released. Similar systems were being tested at the Bunker Hill and Page Mines but were not widely adopted. The Mine Owners Association instead installed a suction dredge at Mission Flats—an approach Ellis acknowledged would reduce, but not eliminate, pollution.
Direct discharge of mine waste into the river finally ended in 1968 with federally mandated water quality regulations and widespread use of settling ponds. Despite these improvements, historic mining left a lasting legacy. Tailings still line riverbanks and floodplains, forming layers several feet deep that resemble sandy beaches but contain contaminated sediments.
Today, elevated blood lead levels in children and ongoing waterfowl mortality continue to be linked to these deposits. Remediation remains complex, particularly in flood-prone areas where recontamination is possible. Nevertheless, progress continues. Recent efforts include remediation of approximately 700 acres at Gray’s Meadow near Black Lake, converting contaminated land into managed functional wetlands. Upcoming projects include pilot river treatments along the Dudley Reach and restoration of the Gleason wetlands.
Until cleanup is complete, residents and visitors are urged to exercise caution when recreating in affected areas. More information about ongoing remediation and public safety is available at cdabasin.idaho.gov.
THE DIRT: Historic pollution study of the Coeur d’Alene Basin Part 3
During the summer of 1933, Dr. Ellis and a team of scientists from the U.S. Bureau of Fisheries launched one of the first systematic investigations into the effects of mine waste on the Coeur d’Alene River system. Their work sought to understand how decades of mining activity had altered the watershed’s chemistry and biology.
The study began with a review of historic and contemporary mining and milling practices, followed by an inventory of aquatic species and a chemical analysis of mine wastewaters. From there, the team conducted laboratory and field experiments to determine how native aquatic organisms responded to contaminated water.
To assess real-world conditions, live dace minnows and long-nosed dace were placed in large wooden live-boxes. One box was stationed offshore of Harrison Beach in Lake Coeur d’Alene, where relatively clean lake water mixed with river water. A second was placed a quarter mile upstream in the Coeur d’Alene River, fully saturated with mine waste. After three days, the results were stark: fish in the lake remained alive and healthy, while all fish in the river box had died, their bodies coated in heavy mucous slime.
The researchers next examined plankton, microscopic crustaceans that form the base of aquatic food webs. Water samples were collected from four locations: the river mouth at Harrison, a quarter mile upstream from Harrison, the river at Dudley, and clean water from Canyon Creek above the mining district. Each sample was settled and maintained at the same temperature in the laboratory, with tap water used as a control.
Plankton exposed to water from a quarter mile upstream died within 18 hours; those in Dudley water survived no more than 36 hours. Approximately 80 percent of plankton in mixed water from the river mouth died within 48 to 72 hours. No deaths occurred in the clean Canyon Creek or tap water samples during the 14-day experiment.
These findings confirmed what fishermen and riverside communities had long suspected: polluted reaches of the Coeur d’Alene River were acutely toxic, capable of wiping out both fish and the microscopic life that sustained the entire aquatic food web.
To pinpoint the cause, Ellis and his team isolated individual components of the waste stream and tested their effects on frogs, turtles, catfish, bass, goldfish, and plankton. Materials examined included milling chemicals, isolated lead and zinc ores, and hard mineral build up that formed on mine tailings exposed along riverbanks and floodplains.
Milling chemicals showed variable toxicity, with the strongest effects occurring near mill discharge points. As these chemicals traveled downstream, dilution from cleaner tributaries reduced their potency. While dangerous near their source, the scientists concluded that milling chemicals alone could not explain the widespread biological collapse observed miles downstream.
Testing of isolated ores revealed clearer patterns. Plankton exposed to lead ore died within 48 hours, while fish survived longer but secreted heavy mucous until lead particles settled out of suspension. Zinc ore, by contrast, produced no deaths and no visible distress.
Yet these results only deepened the mystery. If milling chemicals weakened with distance and raw ores failed to explain the river-wide devastation, what was causing such severe and persistent toxicity throughout the watershed?
That question led Ellis and his team to focus on a far more dangerous culprit—one formed not in mills or tunnels, but along the riverbanks themselves. Stayed tuned for the final installment of the Ellis Report findings.
