COEUR d’ALENE — The health of Lake Coeur d’Alene is improving, or at least stable, Dr. Craig Cooper said Wednesday.

“We’re starting to see the lake respond to changes in the rivers,” he said to the Four County Natural Resources Committee.

Cooper, senior limnologist and water quality specialist with the Idaho Department of Environmental Quality, reviewed the National Academy of Sciences report on the health of Lake Coeur d'Alene and its tributaries.

He also offered a look at plans to protect the lake.

In a key point about the NAS findings, Cooper said metals and phosphorus from rivers flowing into Lake Coeur d’Alene — the Coeur d’Alene and the St. Joe — are declining.

“What comes into the rivers really controls what comes into the lake,” he said to about 30 people at the Iron Horse restaurant.

Cooper said that since the 1990s, zinc and cadmium have been declining in the northern part of the lake. While lead rose for a time, it is beginning to decline. Phosphorous also went up but “might now be starting to decline.”

“The lake is responding to these changes,” according to a report summary.

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.

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 National Academies of Sciences, Engineering and Medicine released a report last year that said Lake Coeur d'Alene is beginning to recover.

Cooper said metals in lake sediments “are a risk,” but there is “too little data for strong conclusions about the future.”

"The story of metals going down depends on which metals and where in the lake,” he said.

His review primarily targeted the northern end of the lake. He said the southern part of the lake “has more productivity, more oxygen problems because of the way the lake is down there.”

Low productivity, such as Priest and Pend Oreille lakes, where waters are clear, is the goal.

Cooper said they want to prevent eutrophication, which is a rise in nitrogen and phosphorus. As algae feeds on nutrients, it spreads and the water turns green.

“Then things that we don’t want to happen, happen,” he said.

Near-shore development remains a concern.

“We do need to shift our monitoring to better track the emerging impact of development in the lake’s near-shore regions,” according to Cooper’s summary.

Cooper said those involved with the lake's health need to work together “in a more integrated way to protect the lake into the future."

Two primary takeaways of his review were a “clear need to reduce input from wastewater treatment facilities; and build an improved, more integrated scientific and institutional structure to better coordinate science, share data and guide management decisions."

He said the DEQ is implementing NAS recommendations through a mix of water quality projects and scientific investments.

One of its initiatives is a pilot study this summer of 20 sites in 10 of the lake's bays.

“The shallow waters are where we expect to see the first lake influences,” Cooper said.

Other DEQ initiatives include continuing monitoring in partnership with the Coeur d’Alene Tribe and launching an interagency science coordination team “to bring together our best technical minds more effectively and work better across institutional boundaries."

Mary Lou Reed, who attended the meeting, was pleased to hear of the efforts on the lake’s behalf.

“I think that all this attention, the lake deserves,” she said. “We just have to keep it up and respond. Not just study.”

Sandy Emerson of the Natural Resources Committee said signs of improvement are welcome and indicate the lake's health is being watched carefully.

“You’ve got to be vigilant,” he said.

Big picture, Cooper said progress has been made in protecting the lake.

“That earns a job well started, not a job well done," he said.