Coeur d’Alene Lake health shows some improvements but by ‘no means out of the woods’

While Lake Coeur d’Alene remains deeply polluted – the legacy of a century of silver and gold mining – a broad review of lake-health data showed decreases in toxins entering the North Idaho lake.

In particular, the level of phosphorous entering the lake – a chemical associated with plant growth – has decreased in the past decade. So have levels of heavy metals, according to a National Academy of Sciences review of 30 years of data. Those findings were presented at the annual Our Gem Symposium, Tuesday in Coeur d’Alene. The original report was released Sept. 30.

Despite that good news, Coeur d’Alene Tribe scientists and leaders warned that the North Idaho lake’s long term health remains precarious. The NAS report found that the lake remains one of the most contaminated in the U.S. Since the 1990s the amount of phosphorous entering the lake has roughly doubled, despite the last decade of improvement. Meanwhile there are an estimated 75 million metric tons of sediment polluted with lead, zinc and other heavy metals.

“Compared to other lakes in the U.S. this is an immensely contaminated lake,” said Samuel Luoma, the chair of the NAS committee and a research ecologist with the John Muir Institute of the Environment at University of California.

He added, “It’s really important that we don’t view this study as an end all. We should view it as a platform to begin the next stage.”

The majority of those metals are in the lake sediment. However, if dissolved oxygen levels in the lake get low enough – a state known as anoxia – those metals could reenter the water column. Phosphorous is a key driver of plant growth and excessive plant growth can lead to anoxic conditions.

“There certainly are some small trends (showing) that it’s getting better,” said CdA Tribal Natural Resources Director Caj Matheson. “But by no means are we out of the woods.”

Matheson doesn’t want the good news to overshadow the still present danger.

“We would like the community to know that, yes things in the short-term are better but the tribe looks at a longer-scale,” said Scott Fields, the water resource program manager for the Coeur d’Alene Tribe.

He added, ‘We would caution that very recent trends in phosphorous are down the lake is still receiving about two times of what it was in the 1990s.”

Human development and logging have led to increased levels of phosphorus and plant growth in the lake, prompting some calls for more strict lakeshore development laws. Kootenai County regulations include a 25-foot shoreline protection buffer prohibiting removal of native vegetation, site disturbance or building a structure other than stairs or docks. The ordinance has not been modified since 1973, according to the Coeur d’Alene Press.

The NAS report was ordered by Idaho Gov. Brad Little in 2019. It’s not the first time the NAS has looked at the lake’s health. In 2005, the NAS published a massive report finding that the U.S. Environmental Protection Agency’s cleanup plan for the Silver Valley was based on “generally sound” scientific and technical principals and that the agency ought to expand its effort to protect residents and wildlife in the basin.

While Lake Coeur d’Alene is included in the federal Superfund site it does not receive Superfund money. Instead, the state of Idaho and the Coeur d’Alene Tribe were given water-quality management authority by the federal government. In 2009, the Idaho Department of Environmental Quality and the CdA Tribe developed a Lake Management Plan.

In 2019 the CdA Tribe withdrew from the Lake Management Plan, due to a perceived lack of action. At Tuesday’s Our Gem Symposium Matheson said the tribe won’t rejoin the LMP, although he did affirm the tribe’s commitment to work with the state and other stakeholders one-on-one.

“The lake management plan is really not adequate at this moment for protecting this lake,” he said. “So we still … are not going to support the Lake Management Plan.”

Kootenai Environmental Alliance executive director Shelley Austin echoed the tribe’s note of caution.

“The thing is the lake itself has some of the highest cadmium zinc and lead in the united states,” she said. “10 times higher than others. That the lake is improving is great news but doesn’t mean we’re OK.”

She also hopes the NAS report gives her organization – and others – “leverage” when advocating for lake health.

Dan McCracken, the Idaho Department of Environmental Quality, said the NAS report showed that it is possible to clean up Lake Coeur d’Alene, even if it’s a slow process. He pointed in particular to ongoing restoration efforts in the Silver Valley.

“My big takeaway for all of this is we’re excited about some recent trends that indicate the kind of work we’re doing to protect the lake can be effective,” he said. “We recognize there is a lot more work to do and our phosphorus loading is still twice what it was in the 1990s.”