Author: Keri St. John
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.
THE DIRT: Part II of Historic Pollution Study of the Coeur d’Alene River Basin
After mounting local and political pressure, the Idaho state legislature authorized a study of the pollution problems created by Silver Valley mines directly discharging waste into area waterbodies. The Coeur d’Alene River and Lake Commission was created to direct the study, and the commission requested the assistance of the United States Bureau of Fisheries who authorized a survey and a team of four fisheries scientists to investigate the issue. The study was to be conducted during the summer months of 1932, with results reported back to the Idaho State Legislature in 1933. Commissioner Cathcart, as the acting Secretary of the Coeur d’Alene River and Lake Commission, began preparing for the Bureau’s research team in the spring of 1932. Cathcart had a fully functional field laboratory constructed inside a boat house in Harrison; he also secured a small boat and vehicle for the team’s day trips and hired a local man familiar with area waterways to guide them. The team, led by Dr. M.M. Ellis, arrived in Harrison on July 9th, and started work the next day.
Ellis and his crew began by surveying the river system and learning about the disposal practices of the mines. He learned that for the first forty years of operation the mills in the district used the jig table method to process their ores. This method was quite inefficient and considerable quantities of lead and zinc ore were lost with these tailings as they were dumped in the river. The jig method produced larger rock particles and a finer rock powder. Due to their larger size and heavier weight, the jig tailings did not travel as far and completely settled out by the time they reached the Mission Flats in Cataldo where the river widened slightly and created a natural sedimentation area. Ellis noted that the entire Mission Flats area, consisting of several thousand acres, was now entirely covered with mining tailings and slimes that had settled out there. He interviewed several steamboat captains in the area who told him 15 to 20 years ago they could drive their steamboats and tugboats to the Old Mission, but the channel and the mainstream became so obstructed by large bars of mine waste and tailings that this could no longer be done. Inundated with so much waste, the river continued to carry enormous amounts of finer tailings into the Lower Basin miles downstream and into Lake Coeur d’Alene.
By the early 1920s all the mills in the district had converted to a much more efficient selective floatation method. While metal recovery rates improved, the floatation method created new issues. First, the ore bearing rock was reduced in ball mills to a tailings powder much finer than the powder formerly created from the jig tables. When mixed with water these tailings became slimy in texture and were called mine slimes by locals. Because of their small particle size, these new tailings did not readily settle out and were carried farther by the river and were also more susceptible to chemical changes. The floatation method also allowed for ore of much lower grade to be profitably handled, which increased mining efforts and thus increased the amount of waste in general. Lastly, the floatation process required the use of chemicals for separation and float substances that promoted bubbling and frothing, all of which presented new pollution problems.
Next, the science team began taking inventory of living organisms throughout the watershed, including the mine impacted sections of the river, Coeur d’Alene Lake, and the nearby Chain Lakes. They also assessed streams and waterbodies within the basin which were not impacted by mining activities. They collected data on fish fauna, bottom species, plant life, and the microscopic phytoplankton and zooplankton which are necessary to sustain fish populations. The primary focus was to assess numbers and types of fauna present in the contaminated waters and compare those to nearby streams and lakes not impacted by the mine waste. No fish or plankton were found in the portions of the river actively carrying mine waste and it was practically devoid of all aquatic animal life. In contrast the nearby unimpacted side streams and sections above the mining district were found to be thriving with aquatic life. In areas where the mine waters mixed with clean water sources, such as the chain lakes of the Lower Basin, species counts also dropped considerably, with no life in the heavily mixed areas, and increasing life as the water became more diluted. It was clear that these waste materials were taking a toll on the Coeur d’Alene River ecosystem, so now the scientist attempted to find out why.
The sheer number of tailings moving through the river system was enough to be deadly to aquatic species, but the chemical make-up of these sediments also played a significant role. The ore deposits in the Coeur d’Alene district are primarily sulfides but when exposed to air, sunlight, and moisture these metals begin changing chemically into sulphates and oxides, making them even more toxic. Area farmers explained that the tailings deposited on their farms and left along the shores of the river after high water events produced toxic, crystalline substances that killed crops and stock, particularly horses, and to some extent cattle, dogs, and chickens. In addition to studying the tailings themselves, chemical analyses of other conditions that impact fish life were completed including measuring dissolved gases, pH levels, and specific conductance of the mine impacted waters versus non-impacted waters. It was determined that mine waste had not greatly disturbed the balance of dissolved gases, relative acidity, or specific conductance, so the absence of aquatic life could not be ascribed to these conditions but rather to the contents of the waste itself.
Check back for Part 3 to see what the scientist found.
THE DIRT: Historic Pollution Study of the Coeur d’Alene Basin
Today, the waters of the South Fork and the main Coeur d’Alene Rivers run clear as they meander across the lush landscape of the Idaho Panhandle, but in the not-so-distant past those waters ran cloudy gray with the discarded tailings and byproducts of mining in the Silver Valley. As one of the most productive mining regions in the country, the Coeur d’Alene District produced record amounts of lead, zinc, and silver ore, but also created vast quantities of waste. Most mine sites were in the deep, narrow gulches of the mountains, making waste storage and disposal difficult. With limited space and minimal flat ground, it became common practice to dispose of the waste rock and mill tailings directly into nearby creeks, which washed much of the waste away. Smaller creeks carried waste to the South Fork, where materials settled and continued to travel downstream, billowing out into the main Coeur d’Alene River channel. Waste began building up and collecting along riverbanks and the bottom of the river, creating sizeable deposits and manmade sandbars down its length. While common and legally permitted, disposing of waste into area water bodies was not welcomed by all, especially those living downstream in the region known as the Lower Basin. An area of rich fertile land, the Lower Basin had been homesteaded by ranchers and farmers to grow crops, rear livestock, and raise their families. These early settlers began seeing dramatic changes to the landscape as mining waste began to infiltrate the area.
Waste material from area mines first reached Lower Basin farms and communities as visible pollution in the 1890s. By 1900 the farmers began to complain that these sediments were causing illness and poisoning crops and livestock. In 1904, sixty-five Kootenai County farmers filed suit against several mining companies seeking more than $1.2 million in damages. In a separate action, they sought a permanent injunction against waste discharged into the river by these companies. The mining companies, represented by the Mine Owners Association (MOA), successfully defended the preferential status of miners’ water rights in the mining district, claiming that the waste was harmless, and offered the economic importance of mining as a justification for their dumping policies. The damage suit ended two years later when the jury was directed to award the farmers one dollar, a far cry from the $1.2 million they originally sought. In anticipation of additional cases, the MOA started a program to indemnify all property owners along the South Fork and the main Coeur d’Alene River against possible future damages. The MOA shared the cost of purchasing overflow and pollution easements, which released companies from all past and future pollution claims.
In 1929, Harrison banker and Kootenai County Commissioner E. O. Cathcart took John Knox Coe, the city editor of the Coeur d’Alene Press, on a boat tour of the Lower Basin to show him the devasted waterways, landscapes, and abandoned farms dotting the banks of the river. After seeing the damage firsthand, Coe began a new campaign effort to abolish the practice of direct discharge disposal in the Silver Valley. Coe published an eight-part series in the Coeur d’Alene Press called “The Valley of Desolation”, documenting the conditions of the Lower Basin and telling stories of ranchers and farmers whose lives were left in ruin following the destruction of their crops and livestock by mine waste. Coe solicited support for his campaign from local civic and outdoor groups as well as local politicians, including Congressmen Burton L. French of the First Idaho District. By March of 1931, this extra attention and mounting political pressure led the state legislature to authorize and finance a study by the Idaho Pollution Commission.
Learn more about how this study influenced past and current cleanup efforts in the Coeur d’Alene Basin in part two of this series.
