Report: Lake CDA improving

Lake Coeur d'Alene is beginning to recover from nearly a century of mining in its watershed, according to a new report from the National Academies of Sciences, Engineering and Medicine released Friday.

Samuel Luoma, chair of the committee who wrote the report, said while the overall water quality of the lake is improving, “there is a long way to go in terms of complete, full recovery.”

He said it is possible for the progress to be reversed, so future monitoring is key, particularly in shallow waters in bays and inlets that can provide early warning signs.

“Is there a new story being told here? You really have to stay on top of it,” he said Friday.

Coeur d’Alene Tribe Chairman Chief Allan said while the report found the lake’s health is improving, there is work to do.

“This is exciting because although we know that the lake has been the heart of the Coeur d’Alene people for thousands of years, we also recognize its importance to the entire region,” he said. “It is critical to the Tribe that we use this NAS report as a starting point that leads to more actions."

A century of mining in the Silver Valley is said to have contaminated over 75 million metric tons of lake sediment with lead, cadmium, arsenic and zinc.

Those metals remain in the lake’s sediment and waters "at much higher concentrations than in most U.S. lakes."

The committee found that in general, metal concentrations are slowly declining and the lake's health is good.

"There is no evidence that phosphorus levels are increasing, that oxygen levels are declining, or that the lake has become more anoxic over time," a press release said.

While much of the lake’s watershed is a Superfund site managed by the U.S. Environmental Protection Agency, the lake’s environmental quality and cleanup is overseen by a Lake Management Plan, implemented by the Coeur d’Alene Tribe and the state of Idaho.

The study by the Committee on the Future of Water Quality in Coeur d’Alene Lake was sponsored by the U.S. Environmental Protection Agency, Idaho Department of Environmental Quality and Kootenai County.

Concerns have been raised that development along the lake’s shores and other factors could increase the level of nutrients such as phosphorus entering the lake.

It is feared that could trigger increased algae growth and result in decreased oxygen levels that "could potentially lead to the release of metals trapped in the lake’s sediment, posing a major threat to ecosystems and human health."

But the report says most data show the lake has adequate oxygen and relatively low levels of nutrients. No evidence was found that oxygen depletion is getting worse in the deeper waters of the northern part of the lake, or in the deeper waters of the southern part.

The report says the Lake Management Plan would benefit from sampling the lake, its rivers and watershed more often and in more places.

Monitoring of shallow waters is also critical, but “It would be time and money,” said Mike Brett, committee member.

The committee examined data collected in the two major rivers, Coeur d'Alene and St. Joe, that flow to the lake, and found:

• Cadmium, lead and zinc entering the south fork of the Coeur d’Alene River have declined over the last 30 years.

• Lead entering the lake from the Coeur d’Alene River is still substantial, and was 1.3 times higher in 2020 compared with the 1990s.

• Phosphorus at monitoring sites in the Coeur d’Alene River, St. Joe River and Spokane River below the lake outlet has declined by about 20% to 30% from 2010 to 2020.

Regarding the lake, the committee also found:

• Zinc concentration is trending downward significantly.

• Cadmium concentrations declined from 2004 to 2020, with virtually all of the decline occurring after 2014.

• Lead concentrations rose slowly between 2003 and 2012, but have declined since then.

• Reduced pH levels in the deeper lake waters could cause the release of zinc from the lake’s contaminated sediments, the report said.

• Metal concentrations in surface waters are declining.

Even if those trends are sustained, the report said it will take waters near the bottom of the lake at least 10 years, and possibly over 100 years, to reach target metal concentrations set by the Lake Management Plan.

Jess Byrne, director of the Idaho Department of Environmental Quality, said conclusions from the study indicate that its management and remediation activities are working.

“We look forward to working in partnership with Gov. Little, the Coeur d’Alene Tribe, and local stakeholders to prioritize this essential work,” he said.

Caj Matheson, director of the Tribe’s Department of Natural Resources, said it will be important for the tribe to increase its project work around the lake as well.

“We are seeing some positive trends, but those trends are short and the report also shows that it is the lake’s oxygen levels that, if they are too low, will trigger the release of those metals from their rest on the bottom of the lake into the main water column,” he said. "These studies will help us better understand all the issues related to this phenomenon.”

Luoma said while the lake’s natural processes will contribute to the cleanup to a point, “persistence with remediation is really important.”

Lynn Katz, committee member, agreed.

“Remediation has done a significant amount of work to slow the release of metals into the lake,” she said.

Gov. Brad Little said he was pleased to see positive water quality trends in Lake Coeur d’Alene.

He said the data will allow the state’s DEQ to strategically implement the $20 million from the Leading Idaho initiative for the lake's health.

“We can continue these positive trends if we all work together,” Little said.

Luoma said one thing is certain: “The future will be challenging. There’s no question about that.”